Last May they told a local radio programme they were lovers. When it ended, a fellow speaker ordered a policeman to arrest them.
They were questioned at Rochester Row police station for two hours.
'We read out a prepared statement saying we were in a loving and consensual relationship and declined to make any further comment,' Mr Greenhalgh said.
'Eventually they decided not to press charges but it was a very harrowing experience. Parliamentarians voting against lowering the age of consent must consider whether they want 16 or 17- year-olds to go through the same thing.'
Mr Greenhalgh, Mr Parry and Ralph Wilde, 20, an international relations student at the London School of Economics, hope to take the Government to the European Court of Human Rights to force it to equalise the homosexual age of consent with that for heterosexuals. They will hear later this year if it will take on the case. The move has already taken place in Ireland.
Jim Edgell, of the Campaign for Homosexual Equality, wants the age of consent reduced to 16 from 21. 'It cannot be right that young gay men are liable to be arrested and locked up for doing things only slightly different from those that heterosexual people can do quite freely,' he said.
'If an 18-year-old man has a sexual experience with a 21- year-old man he is committing an offence and could go to jail for two years. But if a man has sex with a girl under 16 she is seen as exploited and cannot be held liable.'
Nick Partridge, chief executive of the Terrence Higgins Trust, wants the age of consent lowered for health reasons; research has shown that 87 per cent of homosexual men have their first sexual experience with another man when it is illegal.
He argues that an equal age of consent would reduce alienation felt by homosexual teenagers and cut suicide rates.
It would also allow sex education to recognise homosexuality and instil safe sexual attitudes. 'The current age of consent does not prevent sexual activity. It just criminalises it,' he said.
Dylan Talpin, 19, of Stratford, east London, wants the law to change. 'I remember going to gay pubs and clubs and being paranoid that a van full of policemen would beat me to death.
'It's not right that you have to look over your shoulder all the time,' he said.
Dr Digby Anderson, of the Social Affairs Unit, a right- wing think tank, is opposed to hasty changes in the law.
'There have been too many glib comments . . . which suggest what is right for one group of people must automatically be right for another without any examination of the rival merits of their ways of life,' he said.
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