Johnson becomes mayor of London

Boris Johnson has already said he aims to tackle crime in London

Boris Johnson has officially taken up the post of London mayor.

Mr Johnson's reign began at midnight, when he accepted the seals of office from predecessor Ken Livingstone, mayor for the past eight years.

Since his win in Thursday's election was announced, Conservative Mr Johnson has pledged to tackle violent crime and said he will work to unite communities.

The new mayor has also said he will make public transport safer and protect taxpayers' money.

On Sunday Mr Johnson attended the Sikh New Year festival, Vaisakhi, in Trafalgar Square, where he pledged to be a "mayor for all London", which he said was "the whole world in a city".

The new mayor had been accused during his election campaign of being a divisive figure who could not represent all of the metropolis, and is expected to attempt to build bridges with the city's ethnic minority groups.

I won't rest 'til we have started to make a difference Boris Johnson

Operation Black Vote's Simon Woolley said Mr Johnson "must now demonstrate that he understands what it means to govern a multi-cultural metropolis" and address issues of poverty.

Speaking at the event in Trafalgar Square Mr Johnson said: "The last few days have been very, very exciting and very, very exhausting, but this is the single most wonderful job in British politics.

"I am going to be a mayor for all London and work to unite communities.

"One of the wonderful things we have got in London is fantastic diversity - we have got the whole world in a city."

The new mayor has also said he will make public transport safer

On the topic of crime, he said: "I certainly think it's extremely important that we get to grips with violent crime, which is going up, and we get to grips immediately with the scourge of so-called minor crime and disorder on the buses and the places in which the mayor is directly responsible."

"I am not pretending we can transform this overnight, but it is the job of the mayor to give a lead, and I won't rest 'til we have started to make a difference," he said.

His aides said he would use his first days as London mayor to start work on key pledges such as 440 police community support officers on the Tube and trains, weapons scanners at stations and a review of the western zone of the congestion charge.

Asked about Mr Johnson's victory in an interview with the BBC, Prime Minister Gordon Brown said he wished him well but the "test" was now what Mr Johnson would do in the job.

Hackney North Labour MP Diane Abbott said he was "an accident waiting to happen".

Mr Livingstone had been London's mayor since the office was introduced in 2000, initially as an independent after being overlooked as the Labour candidate. He was welcomed back into the party in 2004, when he won a second term.