David Cameron scrambles to beef up puny EU deal

Charles Grant, the director of the Centre for European Reform, a pro-EU think-tank, is among those warning that unless Mr Cameron can have the brake codified in the treaties it will be open to challenge, potentially muddying the waters of any referendum campaign.

"Getting treaty change on the in-work benefits brake is crucial for Cameron because he will almost certainly be challenged before the European Court of Justice on this, given that some will claim it is discriminatory. He needs treaty change and the Poles are pivotal on this," he said.