British Prime Minister David Cameron sought to quell fresh signs of rebellion in his Conservative Party over Europe, warning ministers they will have to back his European Union strategy or leave his government.

Speaking on the sidelines of a meeting in Germany of the Group of Seven Industrial nations (G7), Cameron, who has pledged to renegotiate Britain's EU ties before offering a membership referendum, signaled he would not tolerate dissent.

"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," he told reporters, when asked whether he would allow ministers to vote according to their conscience

"Everyone in government has signed up to the program set out in the Conservative manifesto."

Senior Conservative lawmaker David Davis said Cameron's stance on ministers was "unwise".

"There is a risk what we may end up doing is turning a decent debate into a bitter argument," Davis told BBC Radio, saying until recently most of the party had been willing to give Cameron the benefit of the doubt over his renegotiation efforts.

"This doesn’t show a great deal of confidence in the outcome of those negotiations that he has to say now my way or the high way, stay and obey the line or leave," said Davis.