Prime Minister David Cameron has urged the Turks & Caicos Islands & British overseas territories to “get their house in order” and sign up to international treaties on tax.
He wrote to the10 territories and crown dependencies, including the Cayman Islands and the Isle of Man, which operates low-tax regimes.
Some critics claim companies hiding their profits for tax avoidance or evasion use such places.
The plea comes ahead of the G8 summit in June, when the UK is expected to push for tighter tax measures.
In Mr Cameron’s letter, “With one month to go, this is the crucial moment to get our own houses in order,”.
“I respect your right to be lower tax jurisdictions… but lower taxes are only sustainable if what is owed is actually paid.”
Apart form the Turks & Caicos, the other 9 territories that received the letter were Bermuda, the British Virgin Islands, the Cayman Islands, Gibraltar, Anguilla, Montserrat, Jersey, Guern-sey and the Isle of Man.
Some have been described by the UK government as having “complex tax arrangements”.
Mr Cameron urged them to sign international protocols designed to allow tax information to be shared more easily between countries, and also to take measures to improve their own transparency.
“Put simply, that means we need to know who really owns and controls each and every company,” he said.
Tax avoidance, where companies operate within the rules to avoid paying taxes, and tax evasion, which is outside the law, have risen high on the political agenda in recent months.
High-profile companies like Google, Amazon and Starbucks have faced criticism in the UK for the low levels of tax, they appear to pay compared with the size of their businesses.
On Sunday, Google’s executive chairman Eric Schmidt defended the company’s tax affairs.
He said the search engine giant “has always aspired to do the right thing”, but added that “international tax law could almost certainly benefit from reform”.
