Racism, not multiculturalism, permeated south London in the late 1960s. In my borough white and Caribbean immigrant children lived next door to each other, went to each other’s birthday parties and played in the same football and cricket teams. But the class teacher at our state primary school beat the black kids ferociously with his cane, demanding that they “get back on the banana boat”.

There was nothing so offensive in David Cameron’s speech on the “failure of multiculturalism” last weekend. Britain’s black Caribbean community received no mention at all – there was no need. The government’s 2009-10 citizenship survey found 85 per cent of people with a black Caribbean background felt they belonged strongly to Britain. Yet here are two remarkable statistics from that survey. Among those with a strong sense of belonging to Britain were 91 per cent of people with a Bangladeshi background and 90 per cent of people with a Pakistani background. So how widespread are the rootlessness and alienation among British Muslims of which the prime minister spoke? Less, perhaps, than he implied.

Unquestionably, a small number of fanatics carry British passports and seek to commit terrorist offences in the name of Islam. But this is a security problem and multiculturalism is a social question. The latter is, at most, no more than one of many causes of the former.