Votes would be cast under a "supplementary vote" system, in which voters list their first and second choices. With this system, the votes of minority groups tend to carry more weight than in a first-past-the- post election.
As a result, the leading candidates are bidding for the widest possible support. Lord Archer, the author; Trevor Phillips, the broadcaster; and the MPs Ken Livingstone, Glenda Jackson and Simon Hughes have all lent their support to the Operation Black Vote (OBV) group, which is trying to increase the political involvement of the capital's blacks and Asians.
Later this month, all of them, bar Ms Jackson, will sit on a panel at a public meeting being staged in Westminster by OBV and another group, Black Londoners for a Strategic Authority.
In the same week, two as-yet unnamed cabinet ministers are expected to meet with OBV representatives to discuss race relations in the capital.
OBV was formed in 1996 to try to increase black and Asian electoral registration and turn-out, which is traditionally low, particularly among the young. According to a survey for Time Out, London's news and events magazine, only half of the capital's black people aged between 18 and 35 are registered to vote.
Now, OBV sees the Government's proposal for a London mayor and a 25-member assembly as the best opportunity in recent years for non-whites to flex their political muscle. This is because, low participation notwithstanding, ethnic minorities form a substantial part of the capital's population. According to the London Research Centre, 24.4 per cent of the capital's inhabitants are black or Asian.
The courting of OBV by possible mayoral candidates began in October when Lord Archer, Mr Livingstone and Mr Hughes took part in an OBV public meeting. After the meeting, Lord Archer invited OBV to join the Greater London forum, his non-partisan committee on increased democracy in the capital.
In the new year, OBV were asked to take part in the YES campaign, which is being chaired by Trevor Phillips and is calling on Londoners to endorse the plans for a mayor and assembly in the referendum on the issue, to be held on 7 May.
Last month, Glenda Jackson helped launch OBV's poster campaign for the referendum and the capital's local elections.
The joint chairman of OBV, Simon Woolley, says he is under no illusions as to why many of the leading prospective candidates are so keen to associate themselves with the group.
He said: "I think the interest we're attracting has little to do with a love for black and Asians communities, but has more to do with the power of the non-white vote. This is the first time in British political history that the ethnic minorities will have had such a strong hand in the electoral process."