Gay men will be allowed to give blood after government restrictions were officially lifted, but only if they haven't had sex with another man in the past 12 months.
A lifetime ban on blood donations by men who've ever had sex with another man was put into place in the 1980s to stem the spread of AIDS.
But following a review by the Advisory Committee on the Safety of Blood, Tissues and Organs, the ban has now been lifted as long as donors fit certain criteria.
Men who have had anal or oral sex with another man, with or without a condom, in the past 12 months, will still not be able to donate, the Department of Health said.
This is to reduce the risk of HIV infections being missed by testing and then being passed on to a patient, SABTO said.
The move will be implemented in England, Scotland and Wales.
"Our priority as a blood service is to provide a safe and sufficient supply of blood for patients. This change gives us an opportunity to broaden our donor acceptance on the basis of the latest scientific evidence," said Dr Lorna Williamson, NHS Blood and Transplant's medical and research director.
"The SABTO review concluded that the safety of the blood supply would not be affected by the change, and we would like to reassure patients receiving transfusions that the blood supply is as safe as it reasonably can be and amongst the safest in the world.
"There has been no documented transmission of a blood-borne virus in the UK since 2005, with no HIV transmission since 2002."
"We welcome this change, which is based on strong new evidence that all the experts are agreed on. These regulations will ensure the safety of blood supply for all of us while also being fair and equal in their application," said Sir Nick Partridge of the sexual health charity Terrence Higgins Trust.
Last year there were 2.1 million donations from about 1.6 million donors in the UK, according to Blood.co.uk.