Mr Paucelle said the EU ambassadors would go despite the illegitimacy of the elections because: "We need to be realistic: the power is in the hands of Khameini and Ahmadinejad, including the nuclear file, and we must negotiate with those in power." He added that: "We will walk right out if Ahmadinejad denies the Holocaust or declares that his regime will destroy Israel."

But in a moment of black comedy, the French diplomat also explained that any walkout could end in confusion.

"Paucelle admitted that since non-Muslims had never before received an invitation to the inauguration ceremony presided over by the Supreme Leader, EU diplomats in Tehran have never entered the building where the event will take place, and so they are not sure how they will stage their walk-out, logistically, should they need to do so. They are worried that the doors may be locked," the US cable said.

In an ironic aside given the Wikileaks scandal, the French diplomat also joked about lack of information security at EU level.

Commenting on EU plans to send junior-level delegates only to an earlier mini-inauguration event on 3 August, he said: "It's hard to keep a secret when 27 nations are involved ... but we are trying."

Mr Paucelle's remarks also showed the games that EU envoys play to keep in with Tehran without looking too much like they are cow-towing to the Islamist regime.

"Paucelle also reported that the German Ambassador will return from his vacation on August 4 to ensure that he will miss the first ceremony," the US cable stated.