The fuse that led to Pierre Lellouche’s extraordinary explosion was lit by David Cameron when he faced losing the Tory leadership election.

Mr Cameron, who was desperate to outflank David Davis on the right, balanced his modernising message with a pledge to leave the EPP federalist grouping in the European Parliament.

Looking back at the 2005 decision one of Mr Cameron’s close allies admitted that he and his team had underestimated the cost greatly.

“He thought it was pretty straightforward — it was intellectually incoherent to be allied to a group whose aims we did not support. I guess we didn’t realise how difficult it was going to be,” he said.

The outburst by Mr Lellouche gives a flavour of the dismay that Mr Cameron’s decision caused Angela Merkel and Nicolas Sarkozy, whose respective parties are senior partners in the EPP.

“You want to be marginalised? Well you go for it,” he said that he told William Hague. “Go away for two to three years, in your political economic situation you’re going to be all by yourself and you’ll come back.”

The impression of a spurned lover is not diminished when one remembers that Sarkozy reportedly begged Mr Cameron to change his mind in four hour-long meetings.

“We want the Conservatives to stay with us. It is important politically. If not, we won’t work with you, even on a bilateral level,” Mr Sarkozy reportedly told Mr Cameron.

The relationship is said to have broken down completely when the Tory leader invited his fellow, youthful leader of the Right to address the 2006 Conservative conference — on the condition that he did not talk about Europe.

Allies of Mr Cameron insist that he will get on “just fine” with President Sarkozy if he is elected Prime Minister. They make no such claim for Angela Merkel. “Does anyone really get on with Merkel?” one said.

The German Chancellor’s fury at the EPP decision continues to colour their relationship. After a bilateral meeting with her French counterpart this year she made a thinly veiled attack on Mr Cameron.

“We refuse to stretch out our hand to those who oppose the [EU] Lisbon treaty ... but who at the same time talk about enlargement,” Ms Merkel said. “Those who want more [Europe] have to co-operate.”

Mr Cameron watered down his Europe policy as far as he dared in the hope of avoiding a “massive Euro bust-up”. He got one anyway.

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