Prime Minister Gordon Brown and German Chancellor Angela Merkel have said the world has "no place" for tax havens.
Speaking before a meeting of finance ministers from the G20 group of countries, they said tax havens and hedge funds must be controlled.
Mr Brown called on every country to apply the same international standards to crack down on these practices.
"We must act to reshape the regulatory system for the new times," the prime minister said.
He added: "Greater international co-operation lies at the heart of all our changes. And so we must bring the shadow banking system into the regulatory system."
The old tax havens have no place in this world
The talks came after Switzerland signed up to the Organisation for Economic Co-operation and Development's rules on bank secrecy. The country had risked being added to a global blacklist of tax havens.
Mr Brown said: "This week Austria, Luxembourg and Belgium have joined Switzerland, Hong Kong and Singapore and others in a worldwide agreement to exchange tax information on request and subscribe to the OECD principles about the exchange of tax information.
"This is a recognition that the old tax havens have no place in this new world. We now call on all countries to apply international standards."
Mrs Merkel said it was vital that the world had no places that could escape supervision. She added that writing up a list of existing tax havens had already yielded positive results.
On Friday night the two leaders shared a social supper and began Saturday with a walk in the grounds of Chequers before heading to Downing Street.
G20 LONDON SUMMIT
World leaders will meet next month in London to discuss measures to tackle the downturn. See our in-depth guide to the G20 summit.
The G20 countries are Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, the United Kingdom, the US and the EU.
Describing Friday night's meeting, BBC political correspondent Vicki Young said: "It was a social occasion and really one of the first chances they have had to spend this kind of time together.
"They apparently stayed up relatively late chatting and then this morning all went for a walk in the grounds of Chequers - so all very amicable.
"But there are tensions behind the scenes - this is all, of course, the build-up to the G20 summit in three weeks' time, Angela Merkel making it pretty clear that she doesn't think any more fiscal stimulus is necessary."
But the Conservatives accused Gordon Brown of using Mrs Merkel's visit to bolster his domestic position.
Shadow chancellor George Osborne said: "Central to Gordon Brown's attempt to draw a political dividing line with the Conservatives in the run-up to the Budget has been his claim that the whole world is signed up to yet more debt-funded fiscal stimulus.
"That plan, which he hoped the G20 summit would provide cover for, is falling apart as it becomes clear that other countries like Germany share Conservative concerns about rising debt levels."
France and Germany have previously said they will make clear that "spending more" is not an answer to the banking crisis on its own.
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