These role models can't reach the hoodies

He is right, too, to address Britain's successful black people as he has this week. Because just as increasing numbers of black Britons have at last broken through to success in every profession - Baroness Scotland, the artist Chris Ofili, private equity boss Damon Buffini, Archbishop John Sentamu, footballers, singers, writers, actors - young black boys and men are meanwhile throwing themselves into the darkest pits of crime and degradation.

This is the conundrum. When there were hardly any such role models, young black males fought harder against low expectations. They didn't carelessly wreck their own lives and the hopes of their parents. So will the example of the new, successful black Britons really make any difference?

It has long been said, and was said again this week by Mr Mandela, that the successful could lift those who were stuck in the desperate underclass. Let them "scale the mountains with you", he appealed to a willing audience at a Mayfair hotel this week. The wise words will resonate with the black great and good - but not, I fear with the lost generations who have grown resentful and who are violently hostile to any black man or woman they see making it in the white man's world.

Unfairly, I think, accomplishment itself is seen as a betrayal of blackness, a lack of authenticity as if to be truly black you have to stay outside society and kick away all norms and aspirations.

Middle-class black people are also accused of abandoning "their own" - again unfairly. When I was in Cape Town a few years back, young black men in the townships said that about Mandela, too. Meanwhile, in the US, life has become perilous for well-heeled African Americans trying to live in neighbourhoods with "their own" who have much less.

Parading such role models may actually be counter-productive in our lawless enclaves. Instead of telling drug dealers and teenage bandits, "you can be like me", concerned black professionals are going to need to dress down and get humble again to connect up with these boys and men - and then painstakingly take them on the long journey back to society.

That takes time and is initially unrewarding and hard. It is not nearly as gratifying as mellifluous words at Mayfair hotels and Westminster ceremonials. But it is the only way the black role models whom Mandela called on this week are going to make any real difference in Peckham or Harlesden.