A common question from taxpayers is:
“How would HMRC know?”
Someone may have received rental income, started selling online or held money in an overseas account. Because HMRC has not contacted them, they may assume that the income has gone unnoticed.
That can be a dangerous assumption.
HMRC receives information from many sources. Some organisations report information automatically. In other cases, HMRC can use statutory powers to obtain data about groups of taxpayers or request specific records during a compliance check.
HMRC can then compare this information with:
- Self Assessment tax returns;
- PAYE records;
- company tax records;
- VAT returns;
- property information; and
- other data already held in its systems.
However, a difference does not always mean that tax has been underpaid.
A bank deposit could be a transfer between accounts. Online sales could involve personal possessions sold for less than their original cost. Money from abroad could represent an inheritance rather than income.
Therefore, HMRC may have information about a transaction without knowing its full context. That is why clear records and supporting evidence matter.
Does HMRC Check Every Tax Return Manually?
No.
HMRC processes millions of tax returns and cannot examine each one in detail. Instead, it uses data and risk analysis to identify returns or taxpayers that may require further review.
HMRC’s own guidance explains that information from tax returns, public sources and third-party data helps it identify where the correct amount of tax may not have been paid.
A possible mismatch may lead to:
- an automated adjustment;
- a letter asking the taxpayer to check their position;
- a request for information;
- a compliance check;
- a discovery assessment; or
- a more detailed tax investigation.
The action HMRC takes will depend on the amount, tax involved, age of the issue and its view of the taxpayer’s behaviour.
1.Previous Tax Returns and HMRC’s Own Records
The first source is information that HMRC already holds.
HMRC can compare a current return with:
- earlier Self Assessment returns;
- PAYE income;
- pension information;
- Company Tax Returns;
- VAT returns;
- Construction Industry Scheme records;
- previous disclosures;
- earlier compliance checks; and
- other tax registrations.
A sudden change may prompt questions.
For example:
- rental income appears for several years and then disappears;
- turnover falls sharply while VAT figures remain high;
- a taxpayer claims expenses that are much larger than in earlier years;
- a business closes, but other records suggest continued trading; or
- someone reports a capital disposal without any related income or ownership history.
A change does not prove an error. Businesses gain and lose customers, properties remain empty and income sources end.
However, where the figures do not appear consistent, HMRC may ask the taxpayer to explain what changed.
2. Employers, Pension Providers and Government Records
Employers report payroll information to HMRC through Real Time Information.
Each time an employer pays an employee, it normally sends HMRC a Full Payment Submission. This can include:
- pay;
- Income Tax deducted;
- National Insurance contributions;
- statutory payments;
- employment start dates; and
- employment leaving dates.
Pension providers also report relevant pension payments and tax deductions.
As a result, HMRC can often identify employment or pension income that does not agree with a tax return.
Government departments and other public bodies may also hold information that helps HMRC understand a person’s financial position, subject to the relevant legal information-sharing rules.
This does not mean HMRC’s records are always correct.
For example, an employer may:
- use the wrong National Insurance number;
- submit duplicated payroll information;
- fail to mark an employment as ended;
- report a correction late; or
- allocate income to the wrong period.
Therefore, if HMRC refers to employment or pension income that you do not recognise, ask for the employer or provider details and compare them with your payslips, P60s and pension statements.
3. Banks, Building Societies and Payment Processors
Banks and building societies report information about interest to HMRC.
HMRC may compare the reported interest with the taxpayer’s return and Personal Savings Allowance position.
It may also obtain other financial information through its statutory information and data-gathering powers.
During a compliance check, HMRC may ask the taxpayer for:
- personal bank statements;
- business bank statements;
- credit-card statements;
- savings records;
- loan statements; and
- explanations of individual transactions.
HMRC can also obtain relevant data from merchant acquirers and similar organisations that process card payments for businesses.
This may help it compare card sales with the turnover reported by a shop, restaurant, tradesperson or online business.
However, HMRC does not have unrestricted, live access to every person’s bank account. Different types of information require different reporting processes or legal powers.
In addition, money entering a bank account is not automatically taxable income.
A credit might represent:
- a transfer between the taxpayer’s own accounts;
- repayment of a loan;
- money received on behalf of another person;
- a gift;
- an inheritance;
- an insurance payment;
- a refund; or
- proceeds from selling a personal item.
If HMRC asks about bank deposits, explain each material item and connect it to supporting evidence.
4. Property Records, Letting Agents and Tenants
Property income leaves several possible information trails.
HMRC may receive or obtain information connected with:
- property ownership;
- purchases and sales;
- Stamp Duty Land Tax;
- letting agents;
- rental payments;
- property advertisements;
- tenancy arrangements; and
- deposits or finance.
HMRC’s data-gathering guidance specifically gives rental income paid by letting agents to landlords as an example of bulk third-party data.
Property information may raise questions where:
- a person owns more than one property but reports no rental income;
- a letting agent reports payments that do not appear on a tax return;
- the taxpayer sells a property without reporting a possible capital gain;
- online advertisements show regular short-term letting activity; or
- the declared rental figure does not match third-party information.
Again, property ownership does not automatically create taxable rental income. A second property may be occupied by a family member without rent, remain empty or qualify for a relief or allowance.
Nevertheless, the taxpayer should keep evidence explaining how the property was used and what income, if any, they received.
Landlords who need to correct undeclared residential property income may be able to use HMRC’s Let Property Campaign, depending on the circumstances.
5. Online Selling and Digital Platforms
People increasingly earn money through websites and apps.
This may include:
- selling goods online;
- renting property or rooms;
- providing transport or delivery services;
- offering freelance work;
- creating digital content; or
- providing personal services.
Under the digital-platform reporting rules, affected platform operators must collect, verify and report information about certain sellers to HMRC. They must also provide sellers with a copy of the reported information.
The information can include:
- the seller’s name and address;
- date of birth or business details;
- tax identification information;
- the amount paid or credited;
- platform fees or commissions; and
- the number of relevant transactions.
However, platform reporting does not create a new tax.
It also does not mean that every online sale represents taxable trading income.
For example, someone may sell unwanted personal possessions. If they sell ordinary personal items for less than they originally paid, they will not usually have made a taxable trading profit.
On the other hand, someone who regularly buys goods to resell for profit may be trading.
The tax position depends on what the person does, why they do it and how regularly they do it—not simply on whether a platform reported their details.
The £1,000 trading allowance may also apply in some cases. However, the detailed conditions should be checked before assuming that no declaration is necessary.
6. Overseas Banks and Foreign Tax Authorities
Holding money or investments abroad does not place them outside HMRC’s reach.
The UK participates in international information-exchange arrangements, including the Common Reporting Standard.
Under these arrangements, overseas financial institutions may report details to their local tax authority. That authority can then exchange relevant information with HMRC.
The information may include:
- the account holder’s name and address;
- tax identification details;
- account numbers;
- year-end balances;
- interest;
- dividends;
- certain investment income; and
- proceeds from the sale of financial assets.
HMRC may compare the overseas information with the taxpayer’s UK return.
A mismatch can arise where someone has not reported:
- overseas interest;
- foreign dividends;
- overseas rental income;
- gains from foreign investments;
- income from an offshore pension or structure; or
- other foreign income taxable in the UK.
However, an overseas account does not automatically produce a UK tax liability.
The position may depend on:
- UK tax residence;
- the nature of the income;
- when the income arose;
- double-taxation relief;
- foreign tax already paid;
- the account holder’s beneficial ownership; and
- the tax rules applying to the relevant year.
The figures reported under international exchange may also use different currencies or reporting periods. Therefore, the taxpayer should reconcile the information carefully rather than assume HMRC’s initial interpretation is correct.
7. Public Information, Third-Party Reports and Social Media
HMRC can also use information that appears publicly or reaches it from another person.
Possible sources include:
- Companies House records;
- business websites;
- online advertisements;
- professional profiles;
- social-media posts;
- property listings;
- press reports;
- court or insolvency records;
- customer or supplier information; and
- reports made through HMRC’s tax-fraud reporting service.
For example, a business may advertise several services online while reporting very little turnover. A landlord may publicly advertise several properties but show no rental income on their return.
Social media can also provide context about business activity. However,
photographs of holidays, vehicles or expensive purchases do not by themselves prove undeclared income. People can fund spending through savings, loans, gifts or non-taxable sources.
Information from a former partner, employee, customer or competitor can also lead HMRC to examine a tax position. HMRC should still test the information rather than treat every allegation as fact.
Nevertheless, a detailed report supported by documents, transaction dates or customer information may trigger further enquiries.
How HMRC Connects the Information?
One item of data may not reveal much on its own.
The risk often becomes clearer when HMRC compares several sources.
For example:
| Information HMRC may hold | Possible question |
| Letting-agent payments but no property pages on the return | Was rental income omitted? |
| Platform sales higher than reported turnover | Was all trading income declared? |
| Overseas interest with no foreign-income entry | Is the interest taxable in the UK? |
| Card receipts higher than business sales | Is turnover understated, or is there another explanation? |
| PAYE income missing from Self Assessment | Was employment income omitted or incorrectly matched? |
| Property disposal without a Capital Gains Tax report | Did the disposal create a taxable gain? |
A mismatch is a starting point, not a final conclusion.
The taxpayer may have a valid explanation. However, that explanation becomes much stronger when documents support it.
Does HMRC Need to Tell You Where the Information Came From?
HMRC will often explain the general reason for its enquiry. However, it may not always reveal every source, internal risk marker or third-party report.
A letter might say that HMRC holds information suggesting the taxpayer received overseas income or online-platform payments without identifying every detail at the start.
If the figures seem unclear, ask HMRC:
- which tax year it is checking;
- which income source concerns it;
- what amount it believes was received;
- whether the figure is gross or net;
- which currency applies;
- whether the information relates to one person or a joint account; and
- how it matched the information to the taxpayer.
This can help identify duplicated, incomplete or incorrectly matched data.
What Happens After HMRC Finds a Difference?
HMRC may first send a letter asking the taxpayer to review their return.
Depending on the circumstances, it may then:
- invite the taxpayer to make a disclosure;
- open a formal compliance check;
- issue an information notice;
- amend a return;
- make a discovery assessment;
- charge interest;
- consider penalties; or
- begin a more serious investigation.
The penalty position often depends on the taxpayer’s behaviour.
HMRC may consider whether the error was:
- despite taking reasonable care;
- careless;
- deliberate; or
- deliberate and concealed.
It will also consider whether the disclosure was prompted or unprompted and how fully the taxpayer cooperated.
Therefore, correcting the position before HMRC contacts you can sometimes produce a better penalty outcome than waiting for HMRC to identify the issue.
Practical Guide: What to Do If You Have Undeclared Income
1. Do not assume HMRC will never find it
Information can reach HMRC months or years after the income arose.
2. Identify every affected tax year
List the income source, amounts received and years involved.
3. Gather the original evidence
Obtain bank statements, platform reports, invoices, contracts, property records and overseas statements.
4. Separate income from non-income receipts
Identify transfers, loans, gifts, inheritances, refunds and other non-taxable amounts.
5. Calculate the correct taxable figure
Gross receipts do not always equal taxable profit. Consider allowable expenses, reliefs and foreign tax.
6. Choose the correct disclosure route
The appropriate method may involve an amended return, the Digital Disclosure Service, the Let Property Campaign, the Worldwide Disclosure Facility or another route.
7. Consider the behaviour carefully
The reason for the error can affect how far back the disclosure must go and the possible penalty range.
8. Do not create false records
Where evidence is missing, use a reasonable reconstruction and explain the method.
9. Keep proof of the disclosure
Retain calculations, correspondence, payment details and HMRC acknowledgements.
10. Correct the process for future years
Update bookkeeping, tax registrations and annual review procedures so the problem does not continue.
Frequently Asked Questions
HMRC does not have unrestricted live access to every bank account. However, banks report certain information, such as interest, and HMRC can obtain further financial information through statutory powers where the legal conditions apply.
Does HMRC know about overseas bank accounts?
HMRC receives financial-account information from many overseas jurisdictions through international exchange arrangements such as the Common Reporting Standard. However, the tax treatment still depends on the taxpayer’s circumstances.
Do online selling platforms report to HMRC?
Affected digital-platform operators must collect and report information about certain sellers. However, being reported does not automatically mean that the seller owes tax.
Is every payment into my bank account taxable?
No. A bank receipt may represent income, but it could also be a transfer, loan, gift, inheritance, refund or repayment. Keep evidence showing what the payment represents.
Can HMRC find rental income?
Yes. HMRC may obtain information from letting agents and other property-related sources. It can also compare property information with tax returns.
Can someone report me to HMRC?
Yes. HMRC accepts reports about suspected tax fraud or avoidance. However, an allegation alone does not prove that tax is due.
How far back can HMRC investigate undeclared income?
The assessment period depends on the facts. HMRC will normally have four years in an ordinary case, six years where careless behaviour caused the tax loss and up to 20 years in certain cases involving deliberate behaviour or failure to notify. Separate extended rules can apply to some offshore matters.
What if HMRC’s information is wrong?
Explain the error and provide supporting evidence. Third-party data can contain duplicated figures, wrong reporting periods or identity-matching errors.
Does undeclared income always mean tax evasion?
No. Income may be omitted because of a genuine mistake, misunderstanding or failure to take reasonable care. Deliberate tax evasion requires a different level of behaviour. The facts matter.
Where to Find Official HMRC Information
Current official sources include:
- HMRC guidance on bulk information and risk analysis, explaining how HMRC uses tax returns, public information and third-party data.
- HMRC data-gathering powers overview, including information obtained from data holders such as letting agents.
- Bank and building society interest returns, explaining financial institutions’ reporting duties.
- Employer Real Time Information submissions, explaining payroll information supplied to HMRC.
- Digital-platform seller reporting, covering the information that affected platforms must collect and report.
- Common Reporting Standard guidance, explaining international exchange of financial-account information.
- Let Property Campaign disclosure guidance, covering disclosures of undeclared residential property income.
- Report tax fraud or avoidance to HMRC, explaining how third parties can submit information to HMRC.
The correct disclosure route and assessment period depend on the type of income, tax years and taxpayer’s behaviour. Therefore, seek professional advice before submitting figures to HMRC.
💡 Key Takeaway
HMRC does not need to rely solely on what a taxpayer enters on their return.
It can compare tax returns with information from employers, pension providers, banks, payment processors, letting agents, digital platforms, overseas tax authorities and public sources.
However, a difference does not automatically prove undeclared income. Third-party data can lack context or contain mistakes.
The strongest response connects each disputed amount to clear evidence. If taxable income has genuinely been omitted, dealing with it before HMRC contacts you may reduce uncertainty and improve the available penalty position.
Need Help?
If you have received income that did not appear on your tax return, Accounts Tax Group can help you establish what should have been declared.
We can review bank transactions, rental income, online sales, overseas accounts and other financial information. We can then calculate the correct position, identify an appropriate disclosure route and communicate with HMRC on your behalf.
If HMRC has already contacted you, do not guess or send an incomplete explanation. Contact us promptly so that we can review what HMRC may know and prepare a clear response.
For further practical guidance, explore our HMRC Insights and Updates.
For regular updates, you can follow our company page on LinkedIn, or explore our in-depth visual guides shared via our director’s profile.
