There are few crimes for which there is no defence. Perhaps the one most frequently perpetrated is the black electorate's lack of political representation. This is nowhere more obvious than in London - where although numbers are high, the grip of non-white politicians on the levers of power is weak.

Even with last year's Labour landslide, a non-white population that makes up a fifth of the electorate returned just five MPs out of 74. History provides little comfort. The Greater London Council, famed for its progressive policies on multi-culturalism, only ever had two black faces at County Hall.

This is strange for a city where football teams regularly field four or five non-white players, where everyone from Jazzy B to Asian Dub Foundation have sharpened the cutting edge of British culture and whose streets have seen some vicious racist murders.

Tomorrow gives Londoners a chance for a change when they vote on the Government's proposals for mayor and a city-wide elected authority. According to the London Research Centre, by 2000 - the year when the new power structure takes office - nearly a third of the capital's population will be non- white.

The changing demographics of the capital has seen the prospective candidates for the mayor's post courting the black vote. At a recent meeting of Operation Black Vote - a group which aims to encourage ethnic minority registration - Simon Hughes, Liberal Democrat MP for Southwark and Bermondsey, proposed a quota system: "If you get a white mayor, you should have a black deputy. Likewise if you get a black mayor, you should have a white deputy."

The Conservative peer Lord Archer said it would be "farcical if the Greater London Authority did not represent the black and Asian communities". Lord Archer, however, told me he does not support "any mechanism" to prevent elections from yielding an all-white authority.

But why should having a black politician matter? At present, the problem is the democratic deficit created between the high-visibility of black Londoners and the low numbers of ethnic minority politicians. This gap will do little to promote a multi-cultural society at ease with itself.

In London, there is much to be uneasy about. The Government's own paper outlining its proposals refers only once to the issue of race - preferring to bandy around phrases like "inclusion". Yet the new constitutional arrangements will see unprecedented powers handed over to the capital's newly-elected representatives.

Eleven members of the GLA will sit on the capital's police watchdog - the Met Police Authority. Distrust between the ethnic minorities and the police remains high. According to the Policy Studies Institute three-quarters of Afro-Caribbeans and 40 per cent of Asians believed "they could not rely on the police to protect them from racial harassment". But if few black people make it onto the GLA, then there is little chance of this view being articulated. The new GLA is also likely to have some say in local regeneration. At present a plethora of bodies dole out pounds 200m a year for "economic development" in London.

The explosive mix of unemployment, urban deprivation and the criminal justice system led to riots in the last decade in Brixton and Tottenham. It may seem extreme to suggest similar tensions are threatening to snap the fabric of London's society, yet only last April, Sikh youths from Southall in west London drove 12 miles down the M4 and rampaged through a mainly Muslim area. The police made fourteen arrests. This internecine violence is hardly surprising given that 40 per cent of Asian youth in Southall are unemployed.

Perhaps the most easily understood political paradox is that highlighted by the Notting Hill question. Will a Labour government hand over responsibility of Europe's largest street festival and celebration of Afro-Caribbean culture to white politicians? Without positive action for ethnic minorities, the answer is likely to be yes.