Accounts Tax Group Logo - 2023

Chartered Certified Accountants
Tax Investigation and Disclosure Specialists

Penalties & Appeals

Taxpayer reviewing HMRC penalty notice relating to undeclared income in the UK

What Are the Penalties for Undeclared Income in the UK?

Sean Davern 3 Aug 2026

Penalties for undeclared income in the UK are not fixed and depend on factors such as how the error occurred, whether it was disclosed voluntarily and the level of cooperation provided. In addition to any penalty, HMRC may also charge the unpaid tax and interest. Taking action before HMRC identifies the issue can often lead to a more favourable outcome.

HMRC correspondence and enforcement process showing risks of ignoring tax letters in the UK

What Happens If You Ignore HMRC Letters? Risks, Penalties and Next Steps

Sean Davern 13 May 2026

Ignoring an HMRC letter does not usually make the problem disappear and can increase the risk of penalties, interest and further enforcement action. However, receiving a letter does not always mean the worst-case scenario has happened. Understanding what type of letter you received and responding appropriately can often help prevent the situation from escalating