David Cameron is expected to attack what he suggests is an underhand and undemocratic stitch-up operation going on to choose the next European president.

He is also set to step up his attack on the leading candidate today, former Luxembourg prime minister, Jean-Claude Juncker who he claims "did not stand anywhere and was not elected by anyone".

The accusations have come after the Prime Minister suffered a blow in his relations with the process' potential kingmaker German Chancellor Angela Merkel.

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The Conservative leader failed to stop the German anti-euro AfD joining the Tory bloc in Brussels.

Mr Cameron released a statement insisting that his party still considered Mrs Merkel's CDU its sister party, but the damage appeared done.

Yesterday a Conservative backbencher, Bob Neill, also announced he would seek to reintroduce a EU referendum bill after coming third in the Commons ballot to allocate private member's bills, through which MPs can bring forward proposed legislation.

In an article, which will appear in the European press today, Mr Cameron accuses certain MEPs of "inventing" a process of coronation "whereby they are trying to both choose and elect the candidate".

Each of the main political groups "did a back room deal" to join forces after the elections to support the candidate from the party that won the most seats.

But this he warns is "nonsense".