Barack Obama has voiced optimism that the London Summit would make 'significant progress in moving in the right direction'. In an interview this week with the Financial Times, the US President said: 'The most important task for all of us is to deliver a strong message of unity in the face of crisis.'

Mr Obama played down talk of a split between the US and the leading continental European economies over the need for a further fiscal stimulus versus more regulation. 'The press has tended to frame this as an ''either/or'' approach. I have consistently argued that what is needed is a ''both/and'' approach. We need stimulus and we need regulation. We need to deal with the problems right in front of us and we also need to make sure we are taking steps to prevent these types of breakdown from happening again.'

'With respect to the stimulus, there is going to be an accord that G20 countries will do what is necessary to promote growth and trade. I think there is a legitimate concern that with most countries already having initiated significant stimulus packages that we need to see how they work. Obviously I admire economists. I have a bunch of them on my staff. But to start making a whole host of plans about next year, without having better information on how the current stimulus efforts are working, is something that I think is of concern.'

The US President’s interview was published as the G20 leaders began arriving in the UK for Thursday's London Summit. One of the first was Mexico’s President Felipe Calderón, on a two-day state visit ahead of the meeting. In a press conference after meeting Gordon Brown in 10 Downing Street on Monday, he praised the work of the British Prime Minister in his pursuit of the international agreement needed for a successful summit. The Mexican President called for a consensus between the developed countries and the emerging markets over issues such as reform of international financial institutions and echoed Mr Brown's sentiment that `Global solutions are needed to a global problem.'

In reply, the Prime Minister said the success of emerging economies was the key to future prosperity. 'Our first test at the G20 summit is restoring growth to emerging market economies. That will require a significant increase in resources to our international institutions. These extra resources will help stabilise financial systems and increase bank lending. I am calling on international institutions today to be properly resourced to ensure that they can help emerging economies to the growth that they need.'

Earlier on Monday Kevin Rudd, the Australian Prime Minister, again expressed optimism about the outcome of the London Summit. Following a meeting with UK Mr Brown in Downing Street, he said: 'Never before in modern economic history have governments of the leading economies cooperated so closely on so grave an economic crisis. It is important to point to the trillions of dollars of economic stimulus which have already arisen from the actions of individual governments in response to the Washington Summit to act together.'

Over the weekend, US Vice-President Joe Biden, speaking at the Progressive Governance Conference in Chile, said  the London Summit would produce tangible results. 'The one thing that we've concluded in the States is that the status quo is not an option.... Things are going to change whether we like it or not.'

And in an interview in Saturday’s Financial Times German Chancellor Angela Merkel said she expected 'good results in all areas' at the London Summit.  'We are coming together to make joint decisions, not to compete against each other. We all want the same thing: to put the world economy back on its feet as fast as possible and to prevent such a crisis from happening again.'