The G20 meets in Washington this weekend amid global economic turmoil. Against this background, Gordon Brown has called for a new international financial architecture. The precedent he cites is the Bretton Woods conference of 1944, which resulted in a historic agreement to stabilise a global economy that had been shattered by depression and war.

Forming policy to cope with today's economic crisis is a monumental task. It is unlikely to be advanced by grandiloquent and misplaced historical analogies. For a start, the summit will take place in the absence of the most important figure in international economic diplomacy over the next few years: President-elect Obama. The financial maelstrom that has swept through the world economy started in the United States. It will be resolved only with American leadership.

Secondly, the temptation to theorise about a new set of supranational institutions is liable to divert attention from less glamorous but more practical concerns. Most urgent, the specifically national failures of UK policy - fiscal mismanagement, poor financial regulation, ever-growing reliance on public and private debt and failure to constrain a damaging asset price bubble - will not be rectified by international agreement. Dealing with them requires leadership at home.

Bretton Woods was important to the recovery of the global economy after 1945, by delivering exchange-rate stability, expanding trade and investment, and creating the IMF and World Bank. But its main significance was its symbolism. The participation of the United States, the world's leading economy, signalled a different approach from the disastrous isolationism and trade protectionism of the interwar years.

Bretton Woods was an agreement for its time, in a different economic climate. Capital flows were far less international than they are now. Governments were more capable of shaping the global economy. The conference was also testament to an immense amount of planning conducted ahead of time, by officials rather than heads of government. Talk of a new financial architecture for a globalised, 21st-century economy is an open invitation for political leaders to engage in grandstanding.

There is certainly a need for global policy co-ordination in tackling the crisis. But it is not necessary to create a new set of institutions for the purpose. Easing monetary policy and injecting liquidity into the Western economies is being done by central banks simultaneously. Bank regulation must be strengthened, in guaranteeing retail deposits and setting more stringent capital-adequacy standards. Using fiscal policy to stimulate demand would work better if it were conducted by the main economies simultaneously - not least because of the risk that economies with weaker public finances will suffer a run on their currencies. And there already exists a mechanism for liberalising international trade, which needs to be reinvigorated after the failures of the Doha Round.

As the pound continues its precipitate decline, Mr Brown might reflect on the issues that are immediately within his power to affect. Investors require reassurance that fiscal expansion now will be paid for later. The multilateral sphere is vital in its own right. It must not be a refuge for national leaders postponing pressing domestic tasks.