Under the Law Commission plans, cohabiting couples will be entitled to lump sums and annual maintenance payments if they split up, and some inheritance benefits in the event of a death.

The changes were criticised by the Church of England, which said it was concerned by any proposals that could “undermine the gift of marriage”.

But David Allison, of the family law group Resolution, said: “This is momentous. For too long cohabiting couples have assumed they have legal rights which simply do not exist.”

Under existing law, a split in a cohabiting couple can leave one of them in financial difficulty. There is no legal redress if the main breadwinner refuses to provide support for their former lover, even if the couple have raised children.

The proposals, however, will stop short of giving cohabiting couples full legal parity with married couples or gays and lesbians who have entered into a civil partnership.

A consultation document, to be unveiled by the government’s legal reform body this week, will recommend basic rights for couples who have lived together for a minimum period of time. Insiders claim there is “consensus” within the legal community that it should be two years.

Agreement has yet to be reached on the qualifying period for unmarried couples with children, but some lawyers believe there should be no minimum threshold in such cases.

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