The UK and French governments have called for sanctions to be imposed on tax havens from March 2010, the Wall Street Journal reported, saying measures could include withdrawing aid and investment.

"And the world should be in no doubt that the writing is on the wall for tax havens wherever they may be," said UK prime minister Gordon Brown at a joint news conference with the French president, Nicolas Sarkozy.

"So we are calling today for a March 2010 deadline for the introduction of sanctions against tax havens - sanctions that could include revising investment policies, imposing taxes on funds held in tax havens, or the withdrawal of aid, and from today that countdown has begun," Mr Brown was reported as saying.

Last month, an Organization for Economic Cooperation and Development meeting on tax havens confirmed that sanctions could be imposed on jurisdictions that don't cooperate on new rules. However, it was left to individual countries to decide those sanctions.

Countries such as the UK, France, Germany and the US have been mounting a legal and rhetorical assault on offshore financial jurisdictions such as Switzerland. Many of the world’s major economies are heavily in debt and keen to claw back money held in offshore accounts. The Swiss banking industry, for example, has accused countries such as the UK – which has its own offshore financial centres – of hypocrisy.

Mr Sarkozy called on tax havens to go even further, and to commit to greater transparency on fiscal matters, the WSJ report said.

"Tax havens have shifted from the black list to the grey list, now fiscal cooperation conventions must be signed...they need to exit the grey list," he said.

In April, the OECD put just four countries on the black-list, more than 30 on the grey-list, who are willing to cooperate more but have so far failed to provide enough transparency, and about 40 countries on a white-list considered fully committed to international standards of information exchange.