The success came despite a final bid by a senior Conservative backbencher to widen the Bill to include siblings and parents and children over 18. Baroness O’Cathain argued that the Bill was discriminatory because it would give inheritance and capital gains tax advantages to same sex couples that were not available to sisters, brothers, parents and children who looked after each other. She said the death of an elderly sibling could often mean the one left faced great hardship and the loss of the family home.

Conservative former Cabinet Minister Lord Tebbit asked the Government for an undertaking “that it will state that it will not make any change to subsequent Budgets to the requirements for inheritance tax, in consequence of this Bill?”

But Home Office Minister Baroness Scotland of Asthal insisted that if the amendment was passed it would wreck the Bill, telling peers “there is a clear distinction between these provisions and those of marriage. “To ask for this Bill to be postponed because we cannot deal with the issues would be to perpetuate injustice.”

Lord Tebbit called for a clear explanation from Lady Scotland adding “you said there was a clear distinction between civil partnerships as envisaged in this Bill and civil marriage. “Would you elucidate now what that difference is?”

Lady Scotland replied: “One of the differences is consummation. “In relation to marriage, for a marriage to be valid it has to be consummated by one man and one woman and there is a great deal of jurisprudence which tells you exactly what consummation amounts to, partial, impartial, penetration, no penetration. “If you wish me to give a dissertation on family law I would be happy to do so. There is no provision for consummation in the Civil Partnerships Bill. “We do not look at the nature of the sexual relationship, it is totally different in nature.”

But Lord Tebbit said that if there was no question of consummation in a civil partnership why couldn’t it be extended to people who have a close family relationships, such as two homosexual brothers?

Lady Scotland said it was improper for those related to one another to enter into a relationship, similar to that of marriage.

The amendment moved by Lady O’Cathain was defeated by 136 to 251, Government majority 115.

The Bill represents a historic step forward for lesbian and gay people in Britain. The bill will now become an act, which is expected to gain royal assent later this year. The first-ever civil partnership ceremonies are expected to take place towards the end of 2005. Until then, training will be conducted across the country's registrar system, while financial systems dealing with tax and benefits will be amended.