European Union leaders say they are increasingly frustrated that David Cameron has not made concrete proposals on reform.
EU Commission President Jean-Claude Juncker's told the European Parliament he "can't say that huge progress has been achieved".
The British Prime Minister's promised a vote on whether or not the country should stay in the EU by the end of 2017.
Mr Juncker has sparked controversy by appearing to say Britain does not need the EU.
"To tango it takes two, as some here know I am not a splendid dancer, but at least I know the rules that have to be observed by others and it needs two to tango, and so we have to dance and our British friends have to dance."