Gordon Brown on Tuesday spearheaded calls for a multi-billion pound "bail-out fund" to prevent the global crisis spreading to more countries, and warned of the need to stabilise economies "across eastern Europe".

Alistair Darling will on Thursday night reiterate the government's call for international action to address the "unprecedented turbulence" in the world economy. The chancellor will use the annual Mais Lecture to signal he is scrapping Mr Brown's golden rules that control borrowing in the short-term. Mr Darling is expected to assert that this reflects changing global circumstances, rather than a failure of past Labour policy.

"Governments all over the world are using approaches that had until recently been consigned to policymaking history. But it is natural that the conduct of policy should evolve. Just as markets change, so should policy," the chancellor will say.

The prime minister on Tuesday urged the oil-rich Gulf states and China to provide "substantial" funding to the International Monetary Fund, before flying to France for talks on an increase to the European Union's bail-out fund.

The government is keen to emphasise the link between global action and domestic voters' interests, as well as portraying Mr Brown as a world leader.

The prime minister said it was "in every nation's interests and the interests of hard-working families in our country and other countries that financial contagion does not spread". While he did not rule out the UK making a contribution, he insisted the "biggest part can be played by the countries that have got the biggest [balance of payments] surpluses".

The IMF's $250bn (£158bn) bail-out fund "may not be enough" to prevent the crisis destabilising more countries, Mr Brown said.

His spokesman added the UK was "looking at a figure in the hundreds of billions of dollars" for the IMF. Mr Brown called for "action on this new fund immediately".

The prime minister will press the case for urgent additional funding from the Gulf states when he flies to the region at the weekend.

Mr Brown's latest bid to influence the world's biggest oil producers is one of several flying diplomatic visits, designed to drum up support for the UK proposals for financial reforms ahead of a next month's summit of world leaders. The prime minister was last night in Paris, where he won support from Nicolas Sarkozy, the French president.

"We need to have ways and means of ensuring the IMF has additional resources to support certain countries, notably emerging countries," Mr Sarkozy said. He also called for an EU rescue fund to help beleaguered economies in eastern Europe to be raised from €12bn to €20bn (£16bn).

Mr Brown will meet Angela Merkel, the German chancellor, on Thursday before his weekend trip to the Gulf. He will call Wen Jiabao, Chinese premier, later this week in a move to persuade the country to increase significantly its contributions to the IMF.

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Prime minister attacks conduct of BBC presenters

Gordon Brown attacked the "inappropriate and unacceptable" behaviour of two BBC presenters, as the broadcaster came under intense political pressure in the row over obscene phone calls, write Jean Eaglesham and Ben Fenton.

The prime minister's spokesman said earlier on Tuesday the furore over lewd phone calls made on air by Jonathan Ross and Russell Brand and left on the answer machine of actor Andrew Sachs was an issue for the BBC and Ofcom, the broadcasting regulator.

But Mr Brown spoke out later during a visit to Paris, condemning the "clearly inappropriate and unacceptable behaviour".

But he also said: "Ofcom have said they will investigate the matter and it is for the BBC, the BBC Trust and Ofcom to take any appropriate action."

The backlash against the broadcast, for which the BBC has apologised amid a flurry of tabloid fury, sent reverberations around Westminster on Tuesday that brought the broadcaster back into the political line of fire. As backbench Tory MPs demanded the sacking of the two presenters, David Cameron, the opposition leader, called for the BBC to be "transparent" about how the pre-recorded programme came to be transmitted. "We need to know who made the decision to broadcast it. How high up the editorial chain did it go?", he said.