SCENARIOS-What can the G20 realistically achieve?

Best outcome for Brown: A strongly-worded commitment to raise spending and do whatever it takes, in a co-ordinated manner, to get the global economy back on track. No public bickering between nations on the best way forward.

Most likely outcome: A firm commitment to act as necessary to restore growth. Some criticism from France and Germany of excessive public spending plans.

Where the G20 stand: The United States, Japan, China and Britain have all voiced support for further fiscal stimulus measures to boost demand -- eager to act now and risk doing too much rather than hesitate and find out later that not enough was done to avoid a slump.

Much of continental Europe has been far cooler, arguing there is already plenty of support in train which should be allowed to work before committing to further spending, given the precarious state of many nations' public finances.

One area of a genuine, growing unity is among global central banks who are either using unconventional monetary policy tools or considering using them as interest rates near zero.

IMF REFORM AND RESOURCES

Best outcome for Brown: A solid commitment to increase the IMF's resources by a large, specific amount of at least double the existing $250 billion (177 billion pounds) with contributions from both old and emerging powers.

A detailed, timetabled agreement on how to make the International Monetary Fund more representative, giving more say to emerging economies such as China, India and Brazil.

Most likely outcome: A solid commitment to double the IMF's coffers, largely based on developed world contributions, but only a pledge to transform international institutions.