The MoD's move came after a sergeant major announced he intended to have a sex change operation. The policy also means army chiefs will have to consider transsexual recruits.

Sergeant Major Joe Rushton, 38, who has served in Northern Ireland and Bosnia with the Royal Electrical and Mechanical Engineers, has been married four times and has a son.

New guidelines for commanders

He now refers to himself as Joanne and has been given a desk job at the Army's personnel headquarters while he undergoes gender realignment.

Sex-change soldiers' roles may be restricted

The revised guidelines have been issued to commanding officers in the Army, the RAF and the Royal Navy and will stress that every transsexual should receive similar treatment.

A Ministry of Defence spokesman said there was no change in policy but the guidelines were being redrafted to clarify the forces' position.

"The Army treats transsexuality the same as any other long-term medical condition," he said.

The document will advise commanders on providing sex-change soldiers with appropriate accommodation, shower facilities and uniform.

But the MoD said transsexuals' duties would be limited by existing guidance on where male and female personnel can operate. For example, women in the army cannot serve in the armoured corps or the infantry.

No change on gays ban

Christine Burns, vice-president of transsexual rights group Press for Change, welcomed the move. But she expressed concern about the Army's possible reaction to Sergeant Major Rushton entering into a relationship.

"Joanne will physically be a woman but legally be a man," Ms Burns said. "Given the Army's ban on homosexuality, it is not clear whether she will be allowed to have sexual relations with a man or a woman - if anyone."

An MoD spokesman said any transsexual service personnel would be treated according to UK law.

He also stressed the guidelines would not affect the armed forces' stance on homosexuality.

"There is a clear difference between homosexuality and transsexuality. Transsexuality is a gender, issue not one of sexuality," he said.

A spokesman for gay and lesbian pressure group Stonewall said the decision seemed "bizarre".