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

Speaking on the sidelines of a meeting in Germany of the Group of Seven (G7) industrial nations, Cameron, who has pledged to renegotiate Britain’s EU ties before holding 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 on Sunday.

“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, or “Brexit”, unless he achieved radical changes in the bloc.

Cameron’s spokeswoman said his comments applied only to the renegotiation period and he had not yet said whether ministers would be allowed a free vote in the referendum itself. She said newspapers who felt Cameron’s warning had covered the referendum period too had “over-interpreted” his words.

Cameron, who has promised to hold the 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 EU, which they joined in 1973.

This doesn’t show a great deal of confidence

He has said he needs the EU to alter its founding treaties so that any changes he secures are safe from legal challenge. Cameron is vulnerable on the home front, commanding a mere 12-seat majority in the 650-seat House of Commons. A rebellion over Europe among his own lawmakers could derail his wider agenda.

Speaking before Cameron’s office tried to clarify his comments, senior Conservative lawmaker David Davis said Cameron’s stance 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.

“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.”

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