If you go to any of the "gay villages" of London, Manchester or Edinburgh on a Saturday night, you will, as you would expect, see lots of homosexuals. In London, there is the traditional trolling up and down Old Compton Street, going from Manto's to Rupert Street to the Yard to the Village to Escape and, finally, to Heaven, saying witheringly in every single one: "God, what a dump – it's like Leeds in here."

But along with those, as you make your unsteady way from bar to bar, you will see plenty of straight people, and particularly straight girls, out on a hen night or a birthday jaunt, tinsel on their heads and their eyes round as saucers at every drag queen or Muscle Mary. Some have co-opted a long-suffering gay friend for the occasion; others just go into the gay bars fearlessly. It's a substantial presence, and on the whole people put up with it.

"Putting up with it" is a fair description of the situation, and in Manchester, the gay clubs and bars have more or less decided to exert their rights, and stop putting up with it. A researcher from Manchester University, looking into the culture of Manchester's "gay village" on Canal Street, has found that the gay businesses and their core constituency feel thoroughly besieged by the number of hen parties, and actively threatened by the groups of straight men who follow in their wake.

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One club, indeed, has taken the step of barring straight people altogether. It isn't the first place to take the step – many of the coolest gay clubs and bars in London wouldn't let unaccompanied straight people in. Before you ask how they can tell, go and look, straight reader, at your wardrobe. Believe me, we can tell.

It seems rather harsh, I know, and I have to stress that I have absolutely nothing against straight people. Some of my best friends are heterosexual, and it gives one a good feeling to see that heterosexuals are so visible everywhere these days, and not always working in the traditional occupations, either. But there is a time and a place for everything, I feel, and straight people should just accept that if some gay bars don't mind them coming in, others will turn them away on the grounds that a gay bar is for gay people.

The truth is that there are all sorts of situations in life where we are admitted on sufferance, or turfed out. I wouldn't expect to get much of a welcome if I turned up to a black hip-hop club in Brixton with seven gawping white friends, after all. That seems to me to be fair enough. And gay people have a great deal of experience in being made to feel unwelcome, in their jobs, at parties, in social circumstances. An openly gay man might have to look around a bit to find a team he could play football with or to find a job where he would feel entirely comfortable.

You might say that people who know what social exclusion feels like shouldn't themselves perpetrate more social exclusion. In theory that it is true, and anyone would prefer to live in a world without walls between cultures. But the number of places where gay people can just relax, and behave in ways straight people take for granted are very few. In London, you can safely hold your boyfriend's hand in the few streets between Shaftesbury Avenue and Soho Square, and that is basically it.

If a straight person asks, "Why can't I come into a gay bar? I'll behave myself," then it seems rather harsh to refuse. And there is no doubt that many, perhaps most, straight people who are happy to go to a gay bar are going to behave themselves. But even well-behaved straight people, in large enough numbers, start to be a bit of a problem.

Every gay person recognises the sorts of bars that start by being gay, get a reputation for being cool, and then attract straight tourists in such numbers that gay people simply stop going there. One such ex-gay bar in Soho lost so much of its trade by this means that they distributed flyers to the effect that "The Fluffy Bar Welcomes All Members of the Colourful and Outrageous Gay Community Especially Drag Queens, Please," but not even homosexuals are as stupid as all that.

Basically, nobody likes being treated as the free entertainment. It is distinctly uncomfortable to go to a gay club with your young man, start snogging on the dance floor and surface to find that a large hen party is rooted to the spot with amazement at this outrageous sight; it would be worse to be subjected to mockery or abuse, and this has certainly started to happen in Manchester's clubs.

If gay people gave in, they would fairly quickly find that the only spaces they could call their own were sex clubs, and that would not be a very civilised state of affairs. When the ordinary behaviour of gay people is accepted and welcomed everywhere, then there will be no need for specifically gay spaces. Until then, go away and leave us in peace. It doesn't honestly seem a great deal to ask.

p.hensher@independent.co.uk