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 an in-out 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 in the referendum according to their conscience.

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

Cameron spoke out after a group of over 50 of his own lawmakers said they were prepared to join a campaign backing a British EU exit, known as a 'Brexit,' unless he achieved radical changes in the bloc. It was the first sign of Eurosceptic revolt since he was re-elected last month.

One member of the same group suggested that up to nine of Cameron's ministers could vote to leave the EU. That could not be independently confirmed.

The same group appealed to the prime minister to let ministers campaign as they saw fit ahead of the referendum.

But Cameron, who has promised to hold the EU referendum by the end of 2017, says he is confident he can get a deal that will allow him to recommend Britons vote to stay in the 28-nation bloc, a club they have belonged to since 1973.

He is vulnerable however. Re-elected with a surprise majority, he commands a mere 12-seat majority in the 650-seat House of Commons. A fully-fledged rebellion over Europe among his own lawmakers could derail his wider lawmaking agenda and cast a cloud over his second term in office.

Some Eurosceptic Conservative lawmakers feel he has framed the referendum question in a that favors a vote to stay in the EU and are also angry he has decided not to impose restrictions on government campaign activity in the run-up to the vote.

Some have even suggested they feel so strongly about the subject that they may try to amend a law going through parliament to enable the referendum to take place.

But Cameron, whose reform proposals have so far had a mixed reception from other EU leaders, made clear he would not put up with any rebellion, especially among his own ministers.

"If I can get a position where Britain would be better off in a reformed Europe, then obviously that's not something the government is neutral about," he said. "It's not a sort of, ‘On the one hand ...on the other hand,’ approach."