UK hails progress in EU reform agenda after Brussels dinner
Downing Street has said it is "making progress" as it argues for reforms to how the European Union works.
EU leaders have agreed to re-evaluate the bloc's agenda after substantial election gains across Europe by populist and far-right parties.
Mr Cameron discussed the poll results and the way ahead at an informal dinner of EU leaders on Tuesday.
The 28 member states have asked EU officials to launch consultations on future policies.
The results of the European Parliament elections have continued to lead to calls for a rethink on the EU's reach and purpose.
Senior Labour backbencher Frank Field said the UK must make clear what it wanted from future negotiations, including restrictions on the free movement of people across the European Union.
"What we ought to be drawing up in this country is what I would call the red and blue lines," he told BBC Radio 4's Today programme.
"Certainly the free movement of labour is part of that but also how law is interpreted and developed by judges way beyond what was originally envisaged.
"There are a whole range of issues I think we need to get clear for serious negotiation. Then those negotiations do need to be put to people in a referendum.
"If those negotiations go well, I think people will vote to stay.
"If they look as though the skirmishes were not serious at all in these renegotiations, then there is a possibility we might actually look for a much looser association."
Despite gains by anti-EU groups, including UKIP in the UK, pro-European parties still won most votes overall.
EU officials said the results of the European elections had shown "a mix of continuity and change" and that the Eurosceptic message from voters was "at the heart" of discussions between leaders.
Herman van Rompuy, president of the European Council, said Tuesday's meeting had been a "useful first discussion" and that EU leaders had agreed on putting the economy at the heart of the group's agenda.
He also told reporters that he would hold talks with the political groups to be formed in the European Parliament on who will be next head of the Commission, the EU's executive arm.
On the latest projections, the centre-right European People's Party (EPP) will be the biggest political group and its candidate is former Luxembourg premier Jean-Claude Juncker.
But the UK, which sees Mr Juncker as too much of an EU federalist, is among those opposed to his nomination.
The foreign minister of Luxembourg suggested EU leaders were not "united" over who should get the job.
"(Cameron) is clearly against Jean-Claude Juncker. And the council... accommodated him nearly 100% yesterday," Jean Asselborn told the Deutschlandfunk radio station.
EU leaders have traditionally named the Commission head on their own, but under new rules they now have "to take account" of the European election results.
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