Your overseas assets are going to be notified to HMRC
The UK has agreed with 100 other countries to exchange information with banks, Trustees, company administrators, insurance companies etc.
When HMRC have this information they will contact every affected individual to check that any and all income from these overseas sources have been declared.
It will start from September 2018 and in the meantime there is a new amnesty for declaring any omissions. While the amnesty is not terribly benign (no immunity from prosecution), it is significantly better than the options if found to have misbehaved. HMRC will be looking for penalties of between 100 and 200% plus a further 60% for extra bad behaviour.
Where this regime differs from previous actions is that HMRC will be checking on everyone for whom they receive information. Apparently the financial institutions making the reports will ensure that they have the right John Smith because he will have provided his tax reference. It remains to be seen whether HMRC can match the information to the right person and could be messy.
Hopefully none of our clients have overseas income that they have not declared. If there are any, a preemptive strike would be infinitely preferable to the s**tstorm that's coming after.