David Cameron faces a confrontation with Tory right-wingers by supporting moves to enshrine in law the United Kingdom’s promise to spend at least 0.7 per cent of national wealth on foreign aid.

The Prime Minister had backed off from putting the commitment into legislation despite Britain last year becoming the first major industrialised nation to achieve the United Nations target.

Although the Conservative, Lib Dem and Labour leaderships all back the move, development campaigners have expressed frustration at the failure to make the target legally binding.

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Mr Cameron’s reluctance has been widely seen as a wish to avoid a clash with backbenchers who are hostile to the move.

But his hand was forced yesterday when a former Liberal Democrat Cabinet minister, Michael Moore, launched a parliamentary bid to put the 0.7 per cent commitment on to the statute book.

Mr Moore came second in last month’s ballot for private members’ bills, which means his initiative has a strong chance of becoming law with Government backing.

The ring fencing of aid spending, which has steadily risen under the Coalition, has been widely criticised by the Tory right.

They argue it should not be given special treatment when austerity measures are hitting areas such as policing, defence and local government.

Mr Moore said: “Since I intend to build on the work of people in our party, in the Conservatives and Labour, I hope the consensus will be maintained and the Bill will pass.”

Mr Cameron’s official spokesman said: “I would expect the Government to take the same supportive position as it has with previous private members’ bills on this issue in this Parliament.”

A similar Bill in 2012 was backed by ministers, but was talked out by the Tory right-winger Peter Bone.

Last night Mr Bone said: “I’m not going to be told by the party how to vote on a private member’s bill. That is absurd.”

Jim Murphy, the shadow International Development Secretary, said: “With this Bill, a vote in Parliament can save lives across the world. British aid makes a huge difference to millions. We should be proud of what our generosity can do for those in need and what it says about us as a country."

MPs will call for nations such as France, Italy and Spain to pay more towards humanitarian support for Syrian refugees.

The Commons international development committee warns Britain’s disproportionate contribution was unsustainable without poverty-stricken parts of the world losing out.