The President of the European Commission faces accusations that his officials gave inaccurate information under oath during an investigation involving an alleged wiretap more than ten years ago when Mr Juncker was Prime Minister of Luxembourg.

Last Monday, investigating judge Eric Shammo began an inquiry into whether officials working for Mr Juncker falsified key evidence for a Parliamentary and then judicial investigation in 2012 and 2013.

The centre of the allegations are based on a transcript of a covert conversation from January 2007 between Mr Juncker and Marco Mille, the then head of Luxembourg security services - the SREL.

The Times reports the inquiry is to determine whether officials working for Mr Juncker were responsible for an incomplete transcript of a covertly recorded conversation which may have disguised his alleged role in phone-tapping.

Mr Mille, who is on trial for illegal phone-tapping, said: “The falsification of evidence and the deliberate deception of parliament, the judiciary and, ultimately, the public are an unbearable attack on the rule of law.”

Mr Juncker was the European Union’s longest reigning government chief after serving as Luxembourg’s Prime Minister from 1995 to 2013.

But, he was forced to resign after junior coalition partners withdraw their support in protest of Juncker’s apparent failure to rein in a secret service spiralling out of control.

The main reason for the resignation was the Parliamentary inquiry in 2012 which said Luxembourg’s security agency illegally bugged politicians and members of the public.

The recent case is brought against three former intelligence officers - including Mr Mille - over telephone eavesdropping on Loris Mariotto.

Mr Mariotto made bizarre claims linking the family of Luxembourg’s Grand Duke to terrorist attacks in the 1980s.

The version of the transcript used in the Parliamentary scrutiny investigation reportedly omits words that might indicate Mr Juncker had authorised the tap on Mr Mariotto.

But, in another version, which is accepted as complete, Mr Juncker replied on two occasions with “yes” or “mhm” - which is interpreted by investigators as meaning that he understood and agreed with what Mr Mille was saying.

This was when the former spy chief reported to him on a lack of progress after to days of phone tapping and potential problems explaining the interceptions to judges.

At one point Mr Juncker indicates he knew about the phone tapping by saying “we were listening”, which was omitted from the 2012 and 2013 investigations.

As Prime Minister, Mr Juncker could have given permission for the phone-tapping but denies doing so.

Mr Mille described the omissions as a “scandalous manipulation”.

He added: “It is not known to us who arranged for the ‘falsification’. It is not insignificant answering this question to ask who benefited from it.”

His complaint of “falsification” by an unknown person in Government led to a criminal investigation being opened on December 4.

His trial was suspended on November 21 after Mr Juncker told the Luxembourg court he would be unable to face cross-examination as a witness.

The trial was postponed the same day Mr Mille lodged his complaint.

Under oath as a witness in the postponed trial in May 2015, Mr Juncker told the magistrate that “there was definitely no permission for a full phone-tapping operation”.

But, the judge confronted Mr Juncker with the unaltered transcript and said: “The conversation is clearly about a phone-tapping operation over a period of two days.”

Mr Juncker denied it and said he had “the impression of a great deal of confusion” from the words used.

According to a judicial witness examination report, Mr Juncker claims he could not remember the conversations with his intelligence chief.

But, Mr Mille says he authorised an “urgent procedure” wiretap.

The former head of SREL operations and defendant in the trail, Frank Schneider, was infuriated by Mr Juncker’s absence from a scheduled hearing for Tuesday last week, which led to the suspension of the proceedings.

He said: “One would think that Juncker would take this seriously. It is, after all, something that caused him to resign his government in 2013 requiring early elections.

“I am certain that if Juncker can come to Luxembourg to speak to students… about the future of Europe as he did in October this year, he could have found two hours during one of the eight proposed dates… to attend court.”

A commission spokesman said: “He is very willing to testify as a witness but it happens that he is also president of the EC, so we have to find a date that matches his institutional obligations.”

The inquiry was opened last week as Mr Juncker met Theresa May for Brexit talks and the scandal threatens the EU President’s reputation at a critical time for the EU.

Mr Juncker has been involved in a wider scandal involving the activities of his countries spies.

The SREL at one point held a file on the majority of residents.

As Prime Minister of Luxembourg, Mr Juncker never hid his views that compromises and deals being worked out in meetings of EU leaders should be protected from public scrutiny, even with lies.

At the height of the Eurozone crisis, he said: “When it becomes serious, you have to lie.”