[2] Media reports alleged tension between Johnson and the national Conservative leadership as well as the Conservative-controlled central government.

[8] Four people initially sought the nomination: Ken Livingstone, Oona King, Seton During and Emmanuel Okoro.

[8] Several Labour politicians such as Peter Mandelson, Tessa Jowell, Sadiq Khan, James Purnell, Lord Sugar, Alan Johnson, Tony McNulty and David Lammy were all touted as potential candidates, but none of these decided to run.

Ken Livingstone had announced his intention to regain the mayoralty in March 2009 and said at the time that he would run as an independent if he failed to gain Labour's nomination, as he had done successfully in 2000.

[10] Prior to the vote, Livingstone gained the support of the GMB and Unite trade unions, as well as the backing of the majority of Labour members in the London Assembly.

[11] On 24 September 2010, the Labour Party announced that Livingstone had defeated King for the nomination by a wide margin, the former mayor gaining 68.8% of the total votes.

[14] Liberal Democrat councillor Duwayne Brooks, a friend of murdered black teenager Stephen Lawrence who was with him when he died, also put himself forward.

[15] Caroline Pidgeon, Floella Benjamin, Joanna Lumley, Brian Paddick and Susan Kramer were also seen as possible candidates [citation needed].

Jeremy Ambache, a former parliamentary candidate for Putney, also put his name down for selection for his party however he did not continue his campaign since he defected to Labour.

Subsequently, the High Court ruled the Liberal Democrats selection process fair and lawful.

[23] He has previously taken part in a televised abortion debate on RT (Russia Today) in his capacity as press officer and was a list candidate for the party in the assembly elections in 2004.

[23][26] On 2 June 2011, an email was sent to all UKIP members from the Executive Chairman setting out a timetable for selection and requesting applications from possible candidates.

[31] Much of the campaign period was focused on the tax affairs of the main two candidates, Boris Johnson and Ken Livingstone.

It is claimed that he had his accountant arranged for his earnings from media work to be channelled into a private company to avoid the 50p top tax rate.

[38] Livingstone's core proposal was for a significant cut in public transport fares, although his ability to fund this was questioned.

[39][40] Jenny Jones launched her mayoral campaign as the Green Party candidate on 16 October 2011[41] with the release of a mini manifesto.

[46] BNP candidate Calos Cortiglia's core policies included free weekend travel on public transport and a minimum five-year prison term for knife crime.

ARPO, ICM, Ipsos MORI, Populus, TNS-BMRB (formerly TNS System Three) and YouGov are members of the British Polling Council, and abide by its disclosure rules.