It means that MPs have ignored the advice of almost all the leading medical and social services associations and have voted for a compromise which gay men believe reinforces discrimination against them. They say the change will have few benefits.
Roger Goode, of the moderate pressure group Stonewall, said: 'It retains the discrimination and it is discrimination which is at the core of the problem.'
It has been more than 25 years since the Sexual Offences Act 1967 partially decriminalised homosexuality and set the age of consent at 21. Now gay men under 18 will still to be forced to conduct sexual relationships in the knowledge that discovery could mean arrest and imprisonment.
They fear enforcement by the police could become tougher, causing the arrest of numerous gay 16- and 17- year-olds.
'Instead of the police having an obsolete law on their books which they are under no pressure to enforce, they will have a fresh law that they may be obliged to uphold. What will matter is the advice given to police and to the Crown Prosecution Service regarding the treatment of 16- and 17-year-olds,' Mr Goode said.
Home Office figures show that in 1992 there were 244 prosecutions for consensual gay sex involving men under 21. Twelve men were imprisoned. But the numbers could now soar.
The vote will have particular significance for teenagers such as Euan Sutherland, 16, who in his campaign for the equalisation of the homosexual and heterosexual ages of consent has openly admitted that he has sex with his boyfriend. Now he faces arrest and prosecution for what he believes is an expression of love.
The decision goes against the advice of an extensive list of medical and social services agencies, including the British Medical Association, the British Psychological Society, the Royal College of Psychiatrists, the Health Education Authority, Barnardos, the British Association of Social Workers and the National Association of Probation Officers.
The debate has centred on whether boys of 16 and 17 are mature enough to make the decision to have homosexual sex. Although the Royal College of Psychiatrists and the British Psychological Society said there was no evidence that boys were less emotionally developed than girls, many MPs clearly remained unconvinced.
Last night's vote means the United Kingdom continues to have one of the highest homosexual ages of consent in Europe. In Italy, Belgium, Luxembourg, the Netherlands and Portugal the limit is 16 for both gays and heterosexuals. France has an equal age of consent at 15 and Spain at 12.
Britain's principal serious newspapers offered widely differing views on lowering the age of homosexual consent. The Daily Telegraph, which last month gave qualified support for it to be 18, this week hardened its attitude and argued against lowering it from 21. The Times supported 18; the Guardian, like the Independent, supported 16.