Germany wants to reach a deal to keep Britain in the European Union but cannot compromise on the 28-member bloc’s core principles, Chancellor Angela Merkel said on Wednesday ahead of an EU summit.

“On the one hand, we want to reach an agreement with which the British government can successfully campaign, in the forthcoming referendum, to remain in the European Union,” she told the Bundestag lower house of Parliament.

“On the other hand, we don’t want to, and we won’t, call into question the core principles of European integration. These include in particular the principle of free movement and the principle of non-discrimination between European citizens.”

Meanwhile, former British Prime Minister John Major said on Wednesday that quitting the EU would leave Britain in a dangerous “splendid isolation” and could lead to the break up of the United Kingdom itself. PM David Cameron has promised to renegotiate Britain’s EU ties ahead of a membership referendum by the end of 2017. While he favours staying in a reformed EU, he has said he rules nothing out if he does not get the changes he wants.

Mr Cameron’s Conservatives have long been divided over Europe, an issue which contributed to the downfall of Mr Major and his predecessor Margaret Thatcher.

“I am sceptical of a great deal of EU policy, but flirting with leaving at a moment when the whole world is coming together seems to me to be very dangerous,” Mr Major said.