Cabinet ministers in Britain will be allowed to break ranks and campaign either to leave or remain in the European Union, once Prime Minister David Cameron has concluded his renegotiations.

A Number 10 spokesman confirmed that ministers will be told this afternoon that their views will be "accommodated," but only after the process of trying to achieve reform is over.

There had been pressure from a number of Eurosceptics within the Cabinet to be able to express their own strongly held views whatever the substance of the concessions.

The ministers most likely to campaign to leave, regardless of what Mr Cameron achieves, are the Northern Ireland Secretary Theresa Villiers and the Leader of the House Chris Grayling.

They could be joined by Iain Duncan Smith, the Work and Pensions Secretary and Justice Secretary Michael Gove.

Tge Home Secretary Theresa May has also taken a strong line on immigration but loyalty to Mr Cameron might compel her and others to fall into line.

He has said if he fails to achieve substantial reform in each of his four "baskets" then he could also campaign to leave.