The President of the European Parliament has called for "clarity" from David Cameron over the reforms he is seeking to Britain's membership of the EU ahead of the in/out referendum promised by the end of 2017.
Martin Schulz's comments appear to reflect growing frustration in Brussels at the Prime Minister's delay in spelling out exactly what changes he wants to see if he is to advocate continued UK membership of the 28-nation bloc.
Technical talks on Britain's renegotiation began in June, but European Commission President Jean-Claude Juncker said on Wednesday that they had so far not made "huge progress", telling MEPs that "it takes two to tango" and "our British friends have to dance".
Mr Cameron arrived in Brussels for talks with Mr Juncker over lunch and a separate meeting with Mr Schulz before joining other EU leaders for a one-day summit of the European Council.
Speaking at a press briefing with Mr Juncker shortly before the PM's arrival, Mr Schulz said: "Both of us have made it quite clear that both the Commission and the European Parliament at all stages are willing to engage in constructive co-operation.
"I hope that, as far as the UK Government is concerned - and certainly with individuals, including David Cameron - we can make steps forward.
"Above all, we need clarity on what we are going to be discussing over the next few months."