Dozens of police stations have lowered the Union Flag and replaced it with a gay rights banner to mark a day of action against homophobia. One police chief said the rainbow flag demonstrated his force's support for homosexuals who felt they were victims of prejudice.

But critics warned that it was dangerous for forces to show support for particular campaigns.

Earlier this year, Britain's most senior policeman ordered his force not to fly any flags in support of individual groups.

Sir Paul Stephenson, commissioner of the Metropolitan Police, instructed officers to remove a rainbow flag which had replaced a Union Flag at Limehouse police station, in East London, to mark Lesbian Gay Bisexual and Transgender history month.

But elsewhere, four forces flew the gay rights flag at the weekend to mark International Day Against Homophobia and Transphobia - the prejudice against transsexuals.

Merseyside chief constable, Bernard Hogan-Howe, helped raise one above his force's Liverpool headquarters, which was lit up with multi-coloured lights.

And all the force's 41 police stations flew the rainbow flag for the day, marking the anniversary of the day that the World Health Organisation removed homosexuality from its list of mental disorders in 1990.

As most stations have only one flagpole, the Union Flag, which they fly for the rest of the year, had to be lowered.

Peter Fahy, chief constable of Greater Manchester, hoisted the rainbow flag above his force's headquarters.

Cheshire Constabulary flew it on one of three poles outside its headquarters. And in Essex it was raised at the force's training college, in Chelmsford. 

Critics believe the gesture could do more harm than good. David Davies, Tory MP for Monmouth, said: 'Showing support for particular campaigns is a very dangerous route for the police.

The job of the police is to enforce the law even-handedly and without prejudice, and we ought to be able to take that for granted.

'If they refused to fly this flag it wouldn't mean they supported homophobia - it's just political correctness.

It's much better for them to say we just fly the Union Flag, otherwise all sorts of groups will want them to fly their flags too.'

Mr Fahy said: 'We are determined to show our support for anyone who feels they have been targeted because of their individuality.'

Other groups were welcome to propose their banners for special events, his force added.