The European Commission President, Jean-Claude Juncker, equated the EU-UK relationship to a "doomed romance heading for a divorce". "People shouldn't stay together if the conditions aren't the same as when things started. It's easy to fall in love but more difficult to stay together", he added. These comments, made in Paris during the weekend, mark the first time any high-ranked European official or politician publicly contemplated the possibility of Britain leaving the EU.

Mr Juncker also said that Brussels' will not be "grovelling" to stop the UK from leaving and the open borders principle in the EU is not up "for debate, dialogue or compromise".

These words represent another blow to Mr Cameron's attempts to renegotiate Britain's EU membership. Westminster has been calling for greater restrictions to the EU free circulation policies, which would involve changing basic European treaties. Mr Juncker explains that "the EU won't change treaties to satisfy the whim of certain politicians", echoing the views already expressed by the German Chancellor Angela Merkel and other prominent European leaders.

Brussels' unwillingness to debate the open borders principle causes a problem in any reform negotiations including Mr Cameron's. His primary demand involves "changing the treaties on the question of immigration", to give national authorities more powers to control the influx of immigration, especially from Eastern European countries.

This point is pivotal to the British Prime Minister, facing increased internal pressure from UKIP and other Eurosceptic forces, rising in popularity mostly because of anti-free circulation views.

This pressure has already forced the British Prime Minister to promise an EU in-or-out referendum, before 2017, in case he wins the next general election, in May.

The leader of UKIP, Nigel Farage, says that if Europe refuses to debate the free movement principle, Britain's exit of the EU will become inevitable following a referendum.

With European leaders scheduled to meet on February, 12, Mr Cameron will have another chance to present his conditions and try to fix what even the European Commission President, Jean Claude Juncker, now considers a "doomed romance."