Jean-Claude Juncker must take urgent steps to explain his role in the illegal Luxembourg wiretap scandal, a former senior intelligence officer awaiting trial in connection with the scandal has told The Daily Telegraph.

Mr Juncker resigned as Luxembourg prime minister in 2013 in the wake of the scandal in which Luxembourg intelligence chiefs were accused of the unauthorised tapping of phones, bugging politicians and keeping some 13,000 secret files.

The 63-year-old European Commission president has denied any wrongdoing, but has been dragged back into the scandal after fresh evidence emerged suggesting that members of his staff had tampered with crucial evidence.

The new evidence, which led to the postponing of a trial of three senior formers members of Luxembourg’s SREL intelligence service, according to The Times, showed that a key telephone transcript had apparently been doctored.

The secretly recorded conversation between Mr Juncker and his then intelligence chief Marco Mille, made in 2007, shows the two men discussing a telephone interception that Mr Juncker denies ever authorising.

Mr Mille and two colleagues - André Kemmer and Frank Schneider - were awaiting trial for violating privacy laws last month, but the case was postponed on November 21 after Mr Juncker notified the court that he was unable to attend as a witness until a later date.