I SOMETIMES wonder if this is what the Weimar Republic felt like. In 1920s Germany, a weak democracy led by politicians who had lost public trust and respect was overwhelmed by extremism of left and right. The streets echoed to terrorist bombs and communal violence. The result was the strong state and a descent into madness.

Of course, things aren't that bad in Britain. For a start, we don't have the hyper-inflation and economic collapse that shattered post-Versailles Germany. Fascism and communism are in the bin - at least in their twentieth-century forms.

But while history doesn't repeat itself, it does have a habit of rhyming with itself. There are disturbing echoes of the past in the political climate post the London bombings.

There has been a lurch toward intolerance, mistrust, unreason and authoritarianism, which can and should be worrying to anyone with a sense of history.

Somewhere between the rise of Islamic fundamentalism and the increasingly authoritarian instincts of New Labour - the modern war party - we are in danger of losing our capacity for civilised and tolerant debate. Suddenly, everyone is shouting at each other, and waiting for the next bombs to go off.

There is a climate of thinlydisguised racialism in the popular press. Every picture of a Muslim cleric or detainee depicts a sneering, leering bearded fanatic - a kind of comic-book villain straight out of John Buchan. There is a striking resemblance between these contemporary depictions of Muslims and the images of Jews circulated by antisemitic journals in Weimar Germany.

Consider the Iraq war, the misuse of intelligence, and how the directorgeneral of the BBC and the chairman of the Board of Governors were sacked for allowing journalists to expose the truth about the how Britain was bounced into this invasion. More than a whiff of Weimar there.

Democratic politics isn't a given - it has to be remade by each generation. Right now it is under threat from new religious extremisms and from a political class which has lost its sense of history.

On the one hand there is an assault on essential democratic freedoms - the right to a fair trial, freedom of speech - from a government which seems unable to understand how important these ancient freedoms are and is contemptuous of Law Lords who try to defend them.

On the other, there is the descent into anger and extremism among young Muslims, seduced by an obscurantist and monolithic Islam which rejects science and democracy and seeks to establish a theocratic dictatorship.

These gloomy musings were prompted by chairing a debate last night at the Edinburgh International Book Festival on multiculturalism.

The panel was composed of leading black and Asian intellectuals who, in their different ways want nothing more of it, multiculturalism that is, and are full of apocalyptic warnings about the alienation of Britain's immigrant communities.

Now, multiculturalism is a kind of barometer of how rapidly things have deteriorated, how quickly attitudes have hardened. It used to be seen as an enlightened and liberal measure;

a celebration of diversity. It was a way of respecting peoples' differences. We were letting people live their lives according to their own faiths. Or so we thought. No-one thought that it was the creation of a new form of apartheid. Yet that is increasingly how multiculturalism is being regarded on both sides of the ethnic divide.

The right believes that immigrant communities are becoming racial beach-heads for an increasingly separatist Islamic "country within a country". That may seem to be paranoid nonsense. But it is a delusion that finds a willing echo among a number of Muslims who seem ready to accept a form of de facto apartheid as a way of defending their religion and their communities from what they believe is an attack from Anglo - Saxon Christians.

Multiculturalism, instead of bringing communities closer, is now being used as a lever to drive them apart. It is a measure of how far down the road to unreason we have travelled, that it is becoming almost impossible now to make the case for racial integration in Britain without being accused of being an Islamophobic or an Anglo-Saxon racial supremacist.

Now, I'm heartily fed-up with paranoid rantings from latter-day Powellites about how this was exactly what Enoch meant by the rivers of blood and how we have to impose the "British way of life" on immigrants.

No-one knows what the British way of life is, anyway. But I'm also fed-up with self-appointed guardians of Islam who accuse me of Paki-bashing because I don't share their faith. In particular, the attitudes to homosexuals, women and non-Islamic religious beliefs expressed by many Muslim clerics.

Call me old-fashioned, but I don't want a politics which is defined by religion, race, ethnicity or inside leg measurement for that matter. I wish the religious zealots on both sides would disappear into a desert for 40 years and sort themselves out in the traditional manner. Britain has been a secular state - give or take the Anglican establishment - for 300 years.

Keep God out of politics.

But according to the Muslim writer, Ziaddin Sardar, there is "a rampant sense among British Muslims of injustice and anger, as well as shock revulsion and fear". The proximate reason for this is British policy in the Middle East coupled with the banning of groups like Hizb ut-Tahrir and the deportation of radical clerics like Omar Bakri Mohammed.

Now, I agree that the government shares a lot of the blame for the rapidly deteriorating climate of race relations in Britain. Tony Blair's "send them home" speech a fortnight ago, in which he promised to expel religious extremists and lashed out at civil libertarians and Law Lords for not supporting detention, deportation and limits to free speech, has been a political disaster. Not least because he did the extremists' job for them.

The war in Iraq - the most misguided military action in modern history - has contributed massively to the problem, not just of international terrorism, but of domestic racial alienation.

However, for all those errors, I do not believe that Tony Blair is racist.

Or that his government is determined to stamp out Islam. It is pressing ahead with Muslim faith schools and outlawing incitement to racial hatred - much against the better judgment of many in the race-relations sector, who fear that faith schools will institutionalise racial and religious divisions, and that it will become illegal for the BBC to make programmes about Islamic extremism.

We need to find a way of re-starting sensible discourse on race relations. Multiculturalism, for all its faults, is where we have to start.

If only because, the alternative - monoculturalism - is too awful to contemplate.

Read Iain Macwhirter also in the Sunday Herald.