Gordon Brown has exhorted Europe to work with America to forge a new "moral" global capitalism.
The Prime Minister insisted that the financial "hurricane" lashing the world offered an opportunity to promote fairness after years of "irresponsibility".
The G20 summit must push towards better and more transparent regulation, as well as signalling "the beginning of the end for offshore tax havens", he said. He also hinted at a bid to get international agreement on rewards for top bankers.
Mr Brown's call came in a speech to the European Parliament in Strasbourg, as he kicked off a five-day globe-trotting tour, laying the groundwork for next week's crunch summit in London.
"Let's be honest with each other," he told the MEPs. "Our global economic system has not just developed but been distorted in ways that run contrary to the values we celebrate and uphold in every other part of our lives.
"Values such as being fair to others and taking responsibility for our actions; honouring hard work and not rewarding irresponsible excess.
"Established limits to markets agreed in one country or region are being overtaken by global competition between all countries, and so I say it is not enough to promote self-regulation: we have to agree international standards of transparency, disclosure and - yes - of regulation."
He went on: "Just as globalisation has been crossing national boundaries, we now know it has been crossing moral boundaries too."
Mr Brown said the world had learned the cost of "unbridled markets", and good societies needed "a strong sense of values".
"I believe that we can, for the first time, agree the big changes necessary for co-ordinated action that will signal the beginning of the end for offshore tax havens and offshore centres," he said.
