Anyone owing tax on income or gains must tell HMRC about any unpaid tax. They then have 90 days to calculate and pay the tax owed.
HMRC has issued guidance to individuals on how this can be done.
HMRC is targeting tax evasion and they use the information they hold to identify “customers” who haven’t declared all their income.
Failure to declare additional taxes will usually result in higher penalties than those charged if disclosure is made. The penalties could be up to 100% of the unpaid liabilities, or up to 200% for offshore related income.
In serious cases HMRC may consider starting a criminal investigation, in line with their criminal investigation policy.
Details can be foound here.
