If you are a tax resident in the UK and not legitimately claiming remittance basis, you need to report your worldwide income & gains.
If you fail to report this in your personal tax return, the penalties vary based on whether or not you are first prompted by HMRC to make the disclosure of your overseas income.
Your penalty is a percentage of the outstanding tax liability relevant to your undisclosed overseas income.
These percentages are:
- Voluntary (no contact from HMRC) - Minimum Penalty = 100%, Maximum Penalty = 200%
- Non-voluntary (after contact from HMRC) - Minimum Penalty = 150%, Maximum Penalty = 200%