US president Barack Obama warned yesterday that agreement at the much-heralded G20 summit in London’s Docklands was essential if the world was to avoid the mistakes which led to the Great Depression of the 1930s.

However hopes of a deal hit a last-minute stumbling block as after French president Nicolas Sarkozy and German chancellor Angela Merkel warned they would not sign up unless there was tougher regulation of financial markets.

At a joint news conference yesterday, they said that it was a “red line’’ issue and that they would speak with “one and the same voice’’ in the talks at the ExCel conference centre today.

While there is a general belief that failure to reach an agreement would be unthinkable –- sending financial markets into a tailspin - Mr Brown may have to endure some tense negotiating.

Police were braced for more G20 violence after nearly 90 people were arrested during a first day of protest marking the summit.

Metropolitan Police Commander Simon O’Brien warned there may be more clashes between officers and demonstrators as their focus moves to the summit meeting itself at the Excel Centre in London’s Docklands.

Masked anarchists smashed their way into a Royal Bank of Scotland (RBS) branch in central London yesterday despite police efforts to stop them.

There were at least 87 arrests and one protester died in scuffles. Four people have been charged with offences.

Eleven people were arrested in connection with possessing police uniforms