David Cameron has told his ministers that they will have to resign if they want to campaign and vote for Britain to leave the European Union, The Telegraph reported.

Risking a major confrontation with members of his Cabinet, Mr Cameron made his strongest comments yet on the subject, and raised the prospect of resignations by a number of Eurosceptic ministers before the vote, which could be held as soon as next year.

At the G7 conference in Germany, Mr Cameron was asked whether he had “absolutely closed” his mind to allowing ministers a free vote. He replied: “I’ve been very clear. If you want to be part of the Government, you have to take the view that we are engaged in an exercise of renegotiation, to have a referendum, and that will lead to a successful outcome.”

When asked whether anyone in Government who opposes that will have to resign, he said: “Everyone in Government has signed up to the programme set out in the Conservative manifesto.”

Downing Street sources confirmed that Mr Cameron would expect any minister who planned to campaign for Britain to leave the EU to resign.