Gordon Brown is to insist that the G20 must force banks to return to "family values" as the crunch summit looms.
With US president Barack Obama arriving in the UK amid tight security, the Prime Minister is to stress that "honesty and fairness" have to be at the heart of financial services.
The call, in a speech to faith and charity leaders at St Paul's Cathedral in London, comes amid reports that 10 tax havens will agree to share information as part of a crackdown on avoidance.
The premier will tell the audience that he understands the "pain" the recession is causing, and set "cleaning up the global banking system" as his top priority.
"In our families we raise our children to work hard and to do their best and do their bit," he will say.
"We don't reward them for taking risks that would put them or others in danger, and we don't encourage them to seek short-term gratification at the expense of long-term value.
"And in Britain's small businesses, managers and owners do not train their teams to invest recklessly, behave secretively or keep their biggest gambles off the books.
"Most people who have worked hard to build up their firm or shop don't understand why any company would give rewards for failure; or how some people have grown fabulously wealthy making failed bets with other people's money.
"And so our task today is to bring the imperatives served by our financial markets into proper alignment with the values held by families and business people across our country - hard work, taking responsibility, being honest, being fair."
Earlier the Prime Minister set out five tests which world leaders will face when they gather for in London on Thursday, and urged them to "rise to the challenge".
