The blood transfusion service today warned against calls to allow gay men to make donations.

National director Keith Thompson told the Scottish Parliament that HIV infection was rising among gay men.

In a letter to the public petitions committee, Mr Thompson said one-third of HIV-infected blood samples are later revealed to be from gay men.

Mr Thompson said: "Safer sex will keep most gay men free from infection, but men who have sex with men are asked not to give blood because they are known to be at an increased risk of acquiring HIV and a number of other sexually transmitted infections, particularly syphilis, many of which are carried in the blood."

A petition by Rob McDowall was lodged with the committee calling for a review to allow healthy gay and bisexual men to donate blood.

Gay and lesbian groups argued that men are allowed to donate blood one year after having unprotected sex with a woman known to be HIV-positive.

They said current rules also allow men to donate one year after having unprotected sex with intravenous drug users or prostitutes.

Mr McDowall's petition was backed by the National Union of Students which branded current rules discriminatory.

The union said people should be assessed on their "participation in high risk activity", rather than their social group.

American and Germany operate similar rules to the UK but Australia, Japan and Hungary defer donation among gay men for one year after sex, campaigners said.