During the past few weeks, as London has endured attack and uncertainty, it has begun to seem to me that another conflict has been taking place - this one between opposing views of the capital itself. On the one hand there is the notion, propagated by the tabloids and sentimentally inclined commentators, that London's response to the bombings resembled nothing so much as a resurrection of the Blitz spirit - the whole city coming together in a concerted spectacle of defiance and comradeship. As the Daily Mirror put it: "We can take it. If these murderous bastards go on for a thousand years, the people of our islands will never be cowed."
Against that perception is the idea, asserted by Ken Livingstone among others, that the threats to London have revealed its true character as a multicultural world city, where 300 different languages are spoken by some seven million people, all of them united by a common argot of tolerance and acceptance of difference.
In other words, this is a debate about whether the spirit of London is a closed one - defiant, dogmatic, them-against-us - or an open one: thriving on diversity, recognising that, for all their distinctions of background and ethnicity, the capital's population is linked by a shared principle of mutual respect.
But this isn't an argument for Londoners alone. It is a debate about Britain. It is a debate that takes place as the Sun campaigns to ban such progressive scholars as Tariq Ramadan. As the police demand powers to detain terrorism suspects for three months without trial and an innocent man is shot dead with seven bullets to the head. It is a debate about the kind of country we live in at the start of the 21st century and what values we hold precious in fragile times.
It should be said that there are flaws with both lines of reasoning. The concept of Britain as a glorious melting pot of ethnicities runs to the glib. It fails to address the point that large parts of Britain are almost wholly white. And that even in cities of significant diversity, such as Bradford, real tensions exist between Asians on one hand and whites and blacks on the other. Indeed, it's important to accept that each successive wave of immigration on to British shores, from the Irish to Caribbeans to Asians, has sparked discord and sometimes violence. Change is difficult, and this is nothing new. As far back as 1601, Queen Elizabeth I was complaining that the influx of "negars and Blackamoores" into her country from Africa threatened the fabric of British culture.
Yet despite the right's predictions of rivers of blood, Britain has not collapsed into anarchy under the weight of immigration. It has thrived. In Britain's cities today it is irrelevant to talk of "host" and immigrant communities, when many black and Asian families are second- and third-generation British-born. Schooled in tolerance by that long history, we have in consequence the most open and diverse national culture in Europe. Even the insidiousness of the Tory campaign during the May election couldn't convince voters it was "common sense" to abandon such a heritage. This is the legacy tapped so successfully by London's Olympic bid team, when it swayed IOC judges in Singapore with the vision of a city that represented the world within its confines. As Newsweek noted recently: "The British capital has let the world in, and become a model for making a 21st-century metropolis work."
That's why the evocation of the Blitz spirit after 7 July seems so anachronistic to my mind. It suggests that, in extremis, we retreat to an innate set of common principles. John Major spoke in July of fundamentalists who hate "the Anglo-Saxon way of life". Like talk of cricket tests and old maids cycling across village greens, this is a phrase that deserves to be tossed on to the scrap heap of history. Because it is not similarity that binds us in Britain today, but difference.
Less than ever can Britons be described in the singular. Our politics is devolved. Our cultures are diverse. We cannot agree on a permanent national monument to crown the fourth plinth in Trafalgar Square. Yet it is because of this, not despite it, that Britain, with its long education in diversity, speaks with one voice at moments such as 7 July.
The danger now comes from those who take such strength as weakness. From those who insist our response to the bombings must be ever-tougher anti-terror laws. And above all, from the bombers themselves. Britain's al-Qaeda supporters, like the 7 July quartet and the terrorists who failed in their attacks two weeks later, share a contempt for the plurality of the modern nation. Radicalised as they may have been by the deprivation in their home towns and the treatment of Muslims abroad, they have taken shelter in the deepest form of reactionism - one that views the multiplicity of cultures in a city like London as a decadence that demands to be purged.
To stand against them we do not need to summon the spirit of a bygone age, only to keep in mind that everyone in modern Britain has the right to be different.
Ekow Eshun is artistic director of the Institute of Contemporary
Arts and the author of Black Gold of the Sun: searching for home in England and Africa (Hamish Hamilton, £17.99)