The independent inquiry into Martin Bashir’s interview with Princess Diana will take at least six months after the BBC appointed a former Master of the Rolls to lead the investigation.

Lord Dyson, one of the most eminent judges of his generation, promised a "thorough and fair" investigation into the circumstances around the 1995 Panorama interview while Tim Davie, the BBC’s director-general, said the corporation was "determined to get to the truth".

A BBC source said the inquiry would not be quick and that although expected to take six months to report it could be longer. The corporation will make available all relevant records held in its archives.

The hiring of Lord Dyson, 77, is a major coup for the BBC in proving it is serious in getting to the bottom of how the interview withDiana was obtained and whether Mr Bashir, the BBC’s current religious affairs editor, broke its guidelines to do so.

Lord Dyson was Master of the Rolls, the second most senior judge in England and Wales, from 2012 to 2016 and before that was a Justice of the Supreme Court.

Earl Spencer, Diana’s brother, is likely to be reassured by the appointment of such a senior retired judge, and the BBC will now hope he co-operates with the inquiry. 

He had called for the independent inquiry earlier this month, saying "sheer dishonesty" was used to secure the interview with the princess. Mr Bashir faked bank statements which he showed to Earl Spencer to gain his trust and encourage him to arrange a meeting with Diana.

The appointment of Lord Dyson will also make it more difficult for Mr Bashir to find an excuse to avoid cooperating, given the judge’s status. Mr Bashir, 57, is currently on sick leave, having suffered Covid-19 and then undergone a quadruple heart bypass. He has said he is too ill to answer questions over his conduct.

In a statement, the BBC also laid out the terms of reference for the inquiry, which will examine the mocked-up bank statements and other alleged lies told to Earl Spencer and Princess Diana; whether Mr Bashir’s behaviour broke editorial guidelines and whether his alleged underhand tactics were instrumental in persuading Diana to give her only interview to a then largely unknown reporter.

The terms of reference for the Lord Dyson inquiry

Lord Dyson will also investigate what senior BBC staff knew at the time and whether its internal inquiry in 1996, which cleared Mr Bashir of wrongdoing and described him as an "honest man, was adequate. 

The alleged cover-up threatens to be hugely embarrassing for Lord Hall, the former BBC director-general who was head of news at the time of the Panorama interview, and other senior executives inside the corporation.

In a statement, Lord Dyson said: "This is an important investigation which I will start straight away. I will ensure it is both thorough and fair."

Mr Davie, who only took charge of the BBC in September and is facing his first major test, said: "The BBC is determined to get to the truth about these events, and that is why we have commissioned an independent investigation. Lord Dyson is an eminent and highly respected figure who will lead a thorough process." 

Senior MPs also welcomed the appointment of Lord Dyson and said any parliamentary inquiry will now await the outcome of his report.

Julian Knight, the chairman of the Digital, Culture, Media and Sport select committee, said: "We will monitor developments as the inquiry goes forward and request to be updated on its progress.

"The DCMS committee has no plans to hold its own inquiry into this matter. However, we will review the outcome and reserve a decision on whether any further action should be taken at that point."

It emerged on Wednesday that Mr Bashir recently presented an epdisoe of celebrity Supply Teacher on the CBBC children’s channel in which he taught children the principles of journalism.

In his autobiography, published last year, Lord Dyson said he was "strongly opposed to Brexit", dismissed a speech by Boris Johnson as "polished but rather pointless" and was highly critical of two recent Justice Secretaries, Chris Grayling – who "never believed access to social justice" was important – and Liz Truss, who he called a "disaster". 

In "A Judge’s Journey", he also wrote of the Queen’s disappointment at the disappearance of gold-plated teaspoons from garden parties at Buckingham Palace and praised Prince William on a visit to his Inns of Court for his "effortlessly royal way" of putting law students at their ease. "I enjoyed talking to him too," Lord Dyson added.