Gay council workers have been criticised for banning their straight colleagues and friends from their Christmas party.

Leading gay activists questioned the decision, which emerged last night, by the Brighton and Hove City Council LGBT Workers Forum. Experts warned it may even have been illegal.

Peter Tatchell, a spokesman for gay rights group OutRage!, said: "I wouldn't feel comfortable with the idea of excluding heterosexual employees and their friends.

"Inclusivity is always best but if some groups of employees want to hold their own Christmas parties I am not going to criticise that.

"Undoubtedly there are still reservoirs of homophobia in our society, even in a generally gay-friendly city like Brighton.

"I suspect the best way to deal with this is by gay and lesbian people mixing in."

The LGBT Workers' Forum party on December 6 at the V2 nightclub offered free entry to the buffet and a cabaret show. But straight people were warned to stay away.

Posters for the event placed across council buildings stated: "The LGBT Workers Forum and its events are designed to be a safe space for Brighton and Hove City Council LGBT workers.

"Please respect that this event is aimed at LGBT workers, their partners and LGBT friends."

A source said: "My two friends both work for the council but dare not say anything as they would, without doubt, be sacked."

The Argus has received three complaints about the party.

Chris Benson, head of discrimination law at Leigh Day & Co, said: "Potentially it is discrimination under the Employment Equalities Sexual Orientation Regulations but the council may have a justification for doing it.

"The legislation makes it unlawful to discriminate against anyone because of their actual or perceived sexual orientation.

"But it is always going to be more difficult for a majority to use legislation which protects minorities and the council could say it is showing it values LGBT staff and allows them to express their orientation."

But gay groups and councillors have rallied around the forum. James Ledward, editor of G-Scene Magazine, said: "This is a reflection of the institutional homophobia in this council for the last 20 years, although the situation is improving."

Arthur Law, co-ordinator of the city's LGBT community forum Spectrum, said he believed the backlash against the party could be explained by the controversial prosecution of city councillor Peter Willows for calling gay men paedophiles.

He said: "The LGBT workers' forum provides a place for people who do not feel comfortable at other Christmas parties."

Councillor Paul Elgood, who has just stepped down as chair of the council's equalities committee, said: "It is not discrimination at all. Different sections of the communities all organise their own parties."

A council spokesman said: "The social event for LGBT staff provides a free venue and buffet but not drinks.

"The event is there to enable a group of minority staff, who may be isolated at their work places, to network and meet other people from across the council."