Hi,
Any foreign bank interest should be declared in a Self Assessment Tax Return each year, regardless of the amount or even if no tax is payable on the interest.
Unfortunately, you cannot lump the last 8 or 9 years interest together and declare it in one tax return.
Please have a look at the guidance for the world-wide disclosure facility below, for your next course of action.
Make a disclosure using the Worldwide Disclosure Facility
Thank you.