German Chancellor Angela Merkel said future changes in the European Union (EU) treaty cannot be ruled out, BBC reported.

“If we’re convinced of the substance we shouldn’t say it’s impossible to change the treaty. We should concentrate on the substance, not too much on formalities,” Merkel told reporters after emerging from talks with British Prime Minister David Cameron who is trying to secure agreement for reform of the EU in line with Conservative manifesto commitments.

He wants other member states to support Britain’s proposed restrictions to migration and benefit rules before holding a referendum on Britain’s EU membership in 2017.

“We would like to be a part of the process that is going on in Great Britain at the moment and we would like to be a constructive partner in this process,” Merkel was quoted as saying.

Cameron said that the changes could only be achieved through treaty change. “Of course it is going to be difficult but the important thing is to get it under way,” he said.

Defying all predictions and speculations, Cameron’s Conservative Party secured a simple majority in the 650-member House of Commons, winning 331 seats in the British general elections, the results of which were declared on May 8.

The British prime minister has been pushing for tougher rules to prevent migrants claiming benefits. He also wants safeguards to protect London in the event of closer eurozone integration.