A deal that commits a fresh wave of so-called tax havens into disclosing the bank details of British taxpayers is due to be signed.
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.
According to the Treasury, the Isle of Man, which was the first non-US jurisdiction to agree to greater exchange of information with the UK, will also extend information to the four other nations involved in the scheme.
It comes ahead of the UK's presidency of the G8, which Prime Minister David Cameron vowed would see tax transparency as a top priority.
Chancellor George Osborne said the agreement marked a turning point in the fight against tax evasion.
"This represents a significant step forward in tackling illicit finance and sets the global standard in the fight against tax evasion," he said.
"I now hope others follow these governments' lead and enter into similar commitments to this new level of transparency, removing the hiding places for those who seek to evade tax and hide their assets."