The time when a song supporting an English football team could be entitled Vindaloo is, alas, long past. Multiculturalism is out of fashion; vague notions of Britishness are in.

When launching the Veritas manifesto, Roberty Kilroy-Silk, a man whose ego is unfortunately far in advance of his political talents, asked the wonderfully British named Winston Mackenzie to pass him a copy of the Daily Mail.

Kilroy-Silk wanted photographic evidence of the huddled masses desperate to infiltrate our borders. It is time to end multiculturalism, he explained, and return to a single British identity – apparently some cultures are simply inferior to we plucky Brits, and we should not be afraid to say so.

Normally the mutterings of a fringe party would be nothing more than a comic sideshow and fodder for the satirists. But while Veritas was enthusiastically taking up the white man's burden, the Tories have been intent on appealing to the "I'm not racist but" vote. The Conservative party is not racist, but it believes enough of the British public might be to make the 'nudge nudge wink wink' of "Are you thinking what we're thinking?" a viable election strategy.

The party's manifesto goes out of its way to note that immigrants have made significant cultural and economic contributions to Britain. As a result, other than numbers and 'fairness', it is surprisingly hard to work out exactly what their problem with the situation is.

So they reach out to those voters that think that something needs to be done about immigration, even if they are not quite sure what and feel ashamed to express it. By remaining so vague, they thus reach out to the maximum number of disaffected voters while making it almost impossible for the other parties to refute their claims without using the R word.

Such vagueness is at the root of the multiculturalism debate. Some rail against it; others passionately defend it; but no-one seems quite sure what it is, to the extent that, in April 2004, the BBC news website ran a feature entitled "So what exactly is multiculturalism?"

Like "choice", "public service reform" and "Al-Quieda", multiculturalism is a slippery term that allows politicians and commentators to express vague philosophical positions without ever having to tie themselves to specific policies. Politics used to have ideology; now it has buzzwords.

Multiculturalism has been used to mean everything from simple respect and tolerance for other cultures, to dark mutterings about the abandonment of all national identity in the name of a misguided relativism. The one thing that all commentators do agree on is that it has something to do with race and its effect on the way people engage with the world.

But why should culture be defined so narrowly in terms of where your grandparents were born? A rather nebulous set of factors shape personality and worldview: religion, politics, education, employment and life experience, as well as race.

If all these things play a part, then why should two people that attended the same school, went to the same university, work in the same field and have similar leisure interests be defined as culturally different, just because one is an Asian Muslim and the other white and secular? Why should a liberal cosmopolitan Guardianista human rights lawyer and a suburban Sun reading manual worker be defined as culturally similar just because they are white? Is race that big a factor that it overwhelms everything else?

Even if you do consider matters of race, Britain has always been divided. Professor Sir Bernard Crick, who chaired the "Life in the UK" report that led to the introduction of citizenship tests, has argued that Britain has always been a multicultural country, simply by virtue of being four nations in one state.

Such a notion makes ideas of "Britishness" just as hard to pin down as "multiculturalism". If Britishness can encompass Robbie Burns and Seamus Heaney, Winston Churchill and Nye Bevan, then why should Dizzy Rascal or Sanjeev Bhaskar present a problem? And if they do not, why should that chap waiting in line at Calais?

When Veritas and the Conservatives talk about immigration, they are appealing to a popular fear of People Who Are Different Coming Here. But, in doing so, they do not acknowledge the differences that already exist.

There may be a gulf between inner city black communities and comfortable suburban English whites, but money and class, as well as race, cause such a gap. There have always been sectors of society that have different, perhaps even incompatible, worldviews. It is only since they have had different skin colours that anyone other than the revolutionary left thought it was a problem.

Kilroy says that he wants a single British culture; Howard talks of the British dream. But Britishness is a strangely empty concept, with no universally understood ideas behind it. Some countries – the US, France, Israel – have narratives that all their citizens can understand. They cannot end social divisions – can anything? – but they do provide an identity to cling to, a sense of unity in times of crisis.

That is what Britain lacks – undefined ideas of what it means to be British are inherently malleable. This can be a strength in terms of assimilation – again, I refer you to Vindaloo – but it allows people to feel all the more threatened by small but insidious change, the sense that things are not quite what they used to be.

A roundtable in last month's Prospect argued that Britain needed that sense of national purpose if people were to be persuaded that it is in their interest to properly fund public services and improve everyone's lives. That there is this need for national unity seems to be the point that Howard and Kilroy-Silk have been making, albeit in a roundabout, opportunistic and mildly xenophobic way.

But you do not create Britishness just by defining the non-British. Whatever the politics of fear do to this election, they will not bring us together.