The blood transfusion service yesterday 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 that one-third of HIV-infected blood samples were 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 were allowed to donate blood one year after having unprotected sex with a woman known to be HIV positive. They said current rules also allowed 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 the current rules discriminatory. The union said people should be assessed on their "participation in high-risk activity", rather than their social group.

America 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.