European Union leaders say they are increasingly frustrated that British Prime Minister David Cameron has not made concrete proposals on reform of the bloc despite all Britain's talk of possibly leaving unless there is fundamental change,

On the eve of a summit of EU leaders where the issue is expected to be only lightly touched upon, EU Commission President Jean-Claude Juncker told the EU Parliament that "I can't say that huge progress has been achieved."

Juncker insisted he wants Britain to remain in the EU but added that "to tango, it takes two. So we have to dance, and our British friends have to dance."

Cameron set off in May to change the way the EU is run and wants to cut the EU's political powers over member states.