World leaders have arrived at the G20 summit in London where they will strive to agree measures to tackle the worst financial crisis since the 1930s.

The G20 is expected to strengthen banking regulation to try to prevent a repeat of the crisis in the future.

Extra efforts to boost economic growth will be pledged, but specific targets on government spending look unlikely.

However, UK Business Secretary Lord Mandelson told the BBC there were still disagreements over a number of issues.

"[Disagreements] persisted overnight," Lord Mandelson told the BBC News channel, particularly over levels of funding for the IMF, regulation of tax havens and measures to boost global trade.

It is understood that Gordon Brown wants to go further than some other leaders on these matters.

"Our Prime Minister is excessively ambitious in what he wants out of this summit," Lord Mandelson said. "A good thing too, because there's absolutely no point in people just coming here and rehearsing old arguments restating old commitments."

The BBC's business editor Robert Peston says the danger with that approach is that the Prime Minister does not get what he wants and the summit is seen as a failure.

Outside the summit, more demonstrations are expected after protests in London's financial district on Wednesday.

One man collapsed and died at the protest, police said, and at least 87 arrests were made.

There is tight security at the Excel Centre in London's Docklands where the summit is being held.

A small group of protesters have also begun to gather at the London Stock Exchange, where a BBC correspondent says they are far outnumbered by the number of police officers.

'Deal close'

Leaders are beginning the day with a working breakfast. Four-and-a-half hours of talks will then begin in earnest.

Five different drafts are circulating at the summit, the AFP news agency reports, citing diplomatic sources.

Currently, the leaders of the world's largest economies are expected to announce measures in the following key areas:

• Strong words on financial regulation, including limits on the activities of hedge funds, which are currently unregulated investment funds

• No new money committed. However, leaders are expected to pledge to do whatever it takes to boost their own economies and emphasise that - globally - $2tn is already being spent to tackle the global recession

• New rules on tax havens. The UK Treasury has confirmed it has reached an agreement with Liechtenstein over reducing secrecy on tax matters

• More money for the International Monetary Fund, which helps countries in financial trouble. Its resources have been depleted by having to help a number of Eastern European nations

• An estimated $100bn to boost global trade, as indicated by Gordon Brown on Wednesday

• There may also be measures to clamp down on bankers' pay, news agencies report.

In the run-up to the summit, the main differences have been between France and Germany, who are seeking stricter regulation of the financial system, and the UK and US, who think extra government spending would do more to ease the crisis.

However, European Commission President Jose Manuel Barroso told the BBC there was a real willingness amongst participants to have "a convergence" at the end of the summit.

"We will have consensus around the two points that sometimes appear as differences: stimulus of the [global] economy and regulation. We need both, it is a question of credibility."

French President Nicolas Sarkozy has threatened to walk out of the meeting if the G20 does not come up with concrete results. On Wednesday, Mr Sarkozy made it clear he was unhappy with the draft agreement.

BBC economics editor Stephanie Flanders says the G20 is close to an agreement, with the main disputes financial rather than ideological.

Extra funds

More money is likely to be given to the International Monetary Fund, to help developing countries in difficulty.

The head of the IMF, Dominique Strauss-Kahn, told the BBC that in addition to increasing funding for his organisation, he thought dealing with banks' toxic assets - which caused the world's credit markets to freeze up - must be a priority.

"I am worried about how the balance sheets are going to be cleared up, this cleansing of the balance sheet is the problem we really need to address now."

The summit is expected to push for closer supervision of hedge funds, private equity firms and derivatives trading. Tax havens are also likely to be targeted.

'Balancing act'

Leaders will release the final communiqué, which outlines their agreement, at around 1530 BST.

"This is by no means the end of the process", BBC chief economics correspondent Hugh Pym warns. "The G20 will need to meet again."

He says the leaders will have a difficult balancing act in presenting the final agreements later on Thursday.

There will have to be a bit of pragmatism over what can and cannot be achieved, our correspondent says, but they must also convey a sense that they really have a vision as to how they can bring economies through this recession.

The recession has worsened since G20 leaders met last November in Washington.

Both the IMF and the World Bank expect the world economy to shrink for the first time in decades this year.

Reporting from from the Excel Centre, BBC business correspondent John Moylan said the summit would be judged a success if the global recession became a short, sharp shock, rather than a very long downturn.

The G20 group of nations is made up of the world's most powerful economies, accounting for 90% of the world's economic output, 80% of world trade and two-thirds of the world's population.

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