Prime Minister David Cameron sought Monday to calm a row over the forthcoming EU referendum after he angered eurosceptics by appearing to suggest that ministers must campaign for Britain to stay in the bloc or quit.
Speaking at the G7 summit in Germany, the Conservative leader said his remarks had been "misinterpreted" and insisted there was "unity" within his party over his plans.
Cameron, who was re-elected last month, is negotiating with European Union leaders to try to change the terms of Britain's membership of the bloc before holding an in-out referendum by 2017.
He told reporters on Sunday that his goal was to "renegotiate, get a deal that's in Britain's interest and then recommend Britain stays in it".
He continued: "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."
The press and eurosceptic Conservative lawmakers viewed his comments to mean that ministers who wanted Britain to leave the EU would have to leave the government.
"It's pretty plain -- there's not much room to interpret -- that anybody who is going to vote against and campaign against continued membership of the European Union would have to leave government," former Europe minister David Davis told BBC radio.
Davis said this was "something of a change" from Cameron's previous position and said it was "rather unwise", predicting that some ministers would likely resign.
At the weekend, a new group of more than 50 lawmakers said they would lead calls for Britain to leave the EU unless Cameron secures major concessions from Brussels.
Their chairman in parliament, lawmaker Steve Baker, said Monday: "If we don't get a sovereign parliament, I would be quite surprised if one or two (ministers) don't resign."
Cameron's office insisted he had yet to decide whether ministers could campaign on opposing sides ahead of the referendum, as was allowed during the 1975 vote on Britain's membership of the European Economic Community.
Speaking in Germany, the prime minister said: "We don't know the outcome of these negotiations, which is why I have always said I rule nothing out."
He denied the referendum was splitting his party, saying: "I think the Conservative party is delighted that we have got a renegotiation, reform and referendum agenda. There's complete unity about that."
After his re-election Cameron undertook a tour of European capitals to seek support for changes such as making it harder for EU migrants to claim benefits in Britain.