The three will argue that English and Scottish law contravenes the European Convention on Human Rights because it discriminates against homosexual men and interferes with their private lives.
Their cases, which are backed by the homosexual and lesbian lobby group Stonewall, are being launched on the 98th anniversary of Oscar Wilde's arrest in London, where he was subsequently prosecuted and imprisoned for homsexuality. Lawyers expect the European Court of Human Rights to take several years before reaching a decision on the issue.
According to Stonewall, Britain has the highest age of consent for homosexuals of any European country with the exception of the Irish Republic and Cyprus, where homosexuality is banned.
Heterosexuals and lesbians are allowed to have sexual relations at 16 in Britain.
The group says that the majority of European countries have a common age of consent for heterosexuals and homosexuals.
In 1991, the last year for which figures are available, 213 homosexuals were prosecuted for under-age sex in England and Wales, with 169 convicted and 13 sent to prison.
Speaking in London on Saturday, Hugo Greenhalgh, 19, and William Parry, 24, two of the three men taking action at the court in Strasbourg, said they faced only a small risk that they would be prosecuted for admitting they slept together.
Mr Greenhalgh, a student at Edinburgh University, said that if the police were 'stupid enough' to arrest them, it would add weight to their campaign.
Nevertheless, the law criminalising sex under the age of 21 'affects everyone by default because it creates a climate of prejudice and fear', according to Mr Parry, who works for a film company.
As a result of the law, it was difficult to discuss safe sex with homosexual teenagers. 'It's literally killing people. It's just not possible to talk about things openly.'
The third man, Ralph Wilde, a 19-year-old student in London, said: 'The law is ridiculous. We are happy with our sexuality. Why should we be treated differently from all our friends?'
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