Tom Freeman and Katherine Doyle are in love and want to tie the knot _ but they don't want to get married.

The 26-year-old Londoners think they should be allowed to have a civil partnership, a form of legal union available in Britain only to same-sex couples.

On Tuesday, after having their application to form a civil partnership rejected by officials at their local town hall in Islington, north London, they said they will go to court to win the right. They are being backed by gay rights activists, who hope a ruling that allows straight couples the right to a civil partnership would mean, in turn, that gay couples have the right to wed.

"The titles of husband and wife and all the things that pop into people's heads when you say you're getting married don't appeal to us," said Doyle, a student. "In our day-to-day life we feel like civil partners _ we don't feel like husband and wife, and we want the government to recognize that."

Marriage and civil partnership are virtually identical in law, and activists argue both should be open to all couples.

"We think it's time there was one law for everyone," said activist Peter Tatchell, who is organizing the "Equal Love" campaign and has lined up eight couples _ four gay, four straight _ willing to take their cases to court.

"Denying heterosexual couples the right to have a civil partnership is heterophobic," he said.

Some legal experts think there is a strong case, because discrimination on the grounds of sexual orientation infringes Britain's human rights law.

"How can the government justify this, when the legal rights attached to each legal institution are identical?" said law professor Robert Wintemute, who is advising the campaign. "For most purposes, the two institutions are identical _ except for the name."

Britain introduced civil partnerships in 2005, giving gay couples the same legal protection, adoption and inheritance rights as heterosexual married partners _ but not the label of marriage.

The Netherlands, Canada, Belgium, Portugal and Spain have legalized same-sex marriage, while Germany, France, Austria and Switzerland have laws similar to Britain's.

The British compromise was welcomed by many. Thousands of couples have tied the civil partnership knot since then, in venues ranging from city halls to the Houses of Parliament.

But for some, the distinction still rankles.

"We really appreciate the civil partnerships," said Sharon Ferguson, a pastor in the Metropolitan Community Church who hopes to wed partner Franka Strietzel but has been turned down for a marriage license. "But particularly because of my Christian faith, it's marriage that I want."