The RBS is one of the beleaguered banks that has been rescued by millions of pounds of state funds. Protesters also converged on the Bank of England in thousands with slogans such as 'Swindlers List', 'Financial Fools day and 'Storm the Banks'.

A security officer was injured when a protester hit him with a large pole, while several people were arrested in various parts of London as world leaders prepared for the one-day G-20 summit that starts on Thursday.

The protests were mainly prompted by anger at bankers' role in the global economic meltdown, resulting in job cuts and major losses in the value of savings and pensions. Protests were also held outside the US embassy against the war in Iraq.

The largest demonstration was held outside the Bank of England, where four protest marches converged. A group of officers was forced to retreat behind metal crowd barriers outside the bank, apparently because of the crush of the crowd in front of them.

Fruits, empty beer cans and other missiles were thrown towards police as red smoke rose above the crowd. One injured protester was seen shouting at police officers who had formed a line in front of them.

Protesters also set up tents outside the European Climate Exchange for a camp aimed at demonstrating their dissatisfaction with the global approach to tackling climate change.

Many shops and businesses closed for the day, while those that remained open were braced for violence.

Protester Adam Lambert, 25, said: "I'm here with the Stop the War Coalition because we think the G20 are not representing the ordinary people in the world. We think they are representing the rich".

"Every day we hear of billions being given to bankers and billions are being spent on wars. We want to demonstrate today to say we are not going to put up with this and the G20 should represent us. I think people are angry and they want to show their anger," Lambert said.

The police stopped and questioned about half a dozen demonstrators who were travelling in an armoured vehicle and dressed in helmets and overalls.

Officers carried out a fingertip search of the vehicles, similar to the Saracen armoured personnel carriers used in Northern Ireland, before releasing them.