A bill was introduced into the House of Lords on Thursday that, if passed, would give gay and unmarried couples the same rights as married couples.

Introduced by Liberal Democrat peer Lord Lester with the support of the gay rights group Stonewall, the bill proposes that couples can register their partnership, allowing them legal rights in areas such as inheritance, tenancies and pension funds, which are automatically enjoyed by married partners.

Speaking to the BBC Radio 4 Today programme, Lord Lester, president of the Liberal Democrat Lawyers' Association, claimed that many people in "common law" marriages falsely believed they automatically had these rights when in fact they do not. He warned that new legislation was required to rectify the disparity, bringing Britain into line with many other democratic countries, although "civil partnerships" would not be the same as marriage.

"Couples who are in long and enduring relationships should be able to have their relationships recognised," he said.

Stonewall's executive director, Angela Mason, said that the current law was "unnecessarily cruel and discriminatory".

She added: "This bill is not about gay marriage. It is about allowing couples in mutually caring relationships to provide for and protect each other."

However, Hugh McKinner, chair of the National Family Campaign, described marriage as "an ideal", and saw Lord Lester's legislation as an "undesirable erosion of the differential between marriage and co-habitation."

He said: "I don't think the way to do that is to have, in effect, a marriage contract for co-habiting couples."

Labour MP for Reading East Jane Griffiths introduced a similar bill in the Commons last year. Although it failed to pass the second reading stage of the bill, she claimed the support of a number of Labour ministers, Conservative backbenchers and the Liberal Democrat party, as well as organisations such as the Law Society and the Police Federation.

In an interview with ePolitix.com, she responded to criticism by religious and family groups, saying: "I think they are misguided- they have no reason to oppose it because it's got nothing to do with marriage. It's not talking about marriage and where legal measures like this have been introduced in other countries in Europe there have been studies done on the effects of marriage, ie. on the rates of marriage, whether fewer people get married, and there has been no effect at all. In France and Germany, where they've had this legislation in the last few years, the numbers of people marrying have stayed exactly the same."