Thousands of couples, carers and siblings who live together face injustice and financial hardship because the existing law does little to prevent such people from losing their home or sliding into poverty if their relationship breaks down or their partner dies

Veteran human rights lawyer, Lord Lester of Herne Hill QC, who will introduce the Bill said: "Sensibly drafted legislation is urgently needed to tackle the vulnerability not only of unmarried cohabiting couples and their children but also co-dependent carers and siblings who live together."

According to the Office of National Statistics one in six couples in the UK co-habit and do not marry and this is predicted to rise to one in four by 2031.

David Allison, Chair of Resolution’s cohabitation law reform task force, says justice for cohabiting couples and co-dependents is long over-due.

"The Government's proposed research won’t even begin until 2010 and if cost was the issue, one has to ask why the Government specifically excluded research on cost from the Law Commission’s original brief. Many other countries, including Canada, Australia and New Zealand already have protection for cohabiting couples. It is high time that Britain had a family legal system fit for the 21st century."

The Bill would apply only to people living in the same household for a minimum period of time in which the parties have provided a financial or other commitment to each other.

Couples could choose to "opt out" of the scheme using a cohabitation agreement provided legal advice is sought by both parties to protect the vulnerable.