A deal that commits a fresh wave of so-called tax havens into disclosing the bank details of British taxpayers will be signed today.
Anguilla, Bermuda, the British Virgin Islands, Montserrat and the Turks and Caicos Islands have all agreed to automatically share information with the UK in a crackdown on tax evasion.
The British Overseas Territories will pass on names, addresses, dates of birth, account numbers, account balances and payment details and the move also extends to some accounts held by trusts.
They will also share information with other G5 nations - France, Germany, Italy and Spain - as part of an international pilot to clamp down on wealthy banking clients who escape paying taxes by hiding their money overseas.
Chancellor George Osborne said the agreement marked a turning point in the fight against tax evasion.