Reuters – 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, signalled 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 programme set out in the Conservative manifesto."

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, commanding 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.

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 that group, which has appealed to the prime minister to let ministers campaign as they see fit ahead of the referendum, suggested up to nine of Cameron's ministers could vote to leave the EU. That could not be independently confirmed.

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.

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

In another move likely to rile Eurosceptics, The Times reported on Monday that campaign spending limits are to be increased by 40 percent for the referendum, raising fears among those planning to campaign for exit that they will be outspent.

Some Eurosceptics have even suggested they feel so strongly 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."