Earl Spencer is “not at all satisfied” with the parameters of the independent inquiry into the Panorama interview with his sister, Diana, Princess of Wales, he has revealed.

The Earl said he had told the BBC that Lord Dyson, a former Master of the Rolls who will lead the investigation, “must be free to examine every aspect of this matter”.

He did not explain what he felt was missing from the terms of reference but one element of the scandal that has not been included is the BBC’s decision to rehire Martin Bashir as religious affairs correspondent in 2016.

Lord Spencer wrote on Twitter: “As I’ve told the BBC this evening, I’m not at all satisfied with the parameters they’ve set around their enquiry into the @BBCPanorama interview with Diana of 25 years ago tonight. Lord Dyson must be free to examine every aspect of this matter, from 1995 to today, as he sees fit.”

Earl Spencer earlier said he felt duty bound “to stand up for” his late sister, because she had asked him to protect her sons. In a television interview he said he felt “passionately” that he had a role to honour her memory.

The Earl made it clear he would never have introduced Bashir to his sister had he not been shown forged bank statements purporting to show several royal courtiers were in the pay of the security services. He also described his unease about the Netflix series The Crown depicting the princess.

Earl Spencer (r) told Alan Titchmarsh that ‘The worry is that people forget it’s (The Crown) fiction’

Credit: ‘Love your Weekend' with Alan Titchmarsh, Sunday November 22, 10am on ITV. Earl Spencer shares his thoughts on The Crown and its portrayal of his late sister, Princess Diana

He told ITV’s Love Your Weekend with Alan Titchmarsh: “I feel it is my duty to stand up for her when I can. She left me, for instance, as guardian of her sons… so I feel there was a trust passed on. “So yeah, I feel very passionately that I have a role to honour her memory.”

The Earl acknowledged both the princess’s children were now grown up and living independent lives but added: “I would always have honoured that incredible entrustment”.

Lord Spencer is understood to have kept in close contact with both his nephews over developments in the Panorama scandal. Both are understood to have backed him in piling pressure on the BBC to appoint a senior judge to lead an independent inquiry into the alleged subterfuge and “sheer dishonesty” allegedly used as Bashir sought to win their mother’s trust.

Diana, Princess of Wales with Prince William and Prince Harry

Before the Earl’s post on Twitter, the Duke of Cambridge had welcomed the appointment of Lord Dyson, to lead the investigation into whether his late mother was coerced into the interview.

The Prince was just 13 when he sat in his housemaster’s study at Eton to witness the moment the princess admitted: “There were three of us in this marriage, so it was a bit crowded.”

Mr Titchmarsh’s interview with Lord Spencer, which will be broadcast on Sunday, took place on Nov 2, barely 48 hours before he revealed he had handed over a “dossier” to the BBC he claimed showed the “underhand methods” adopted by Bashir to play on the princess’s insecurities.

In the show, he was asked if he felt uneasy watching his sister’s portrayal on The Crown. He said: “A bit. Actually, The Crown asked if they could film at Althorp and I said obviously not. The worry for me is that people see a programme like that and they forget it is fiction. They assume, especially foreigners. I find Americans tell me they have watched The Crown as if they have taken a history lesson. Well, they haven’t.”

He said his own experience of being part of royal history had made him more determined to be accurate when undertaking historical research for his book The White Ship, which charts the chaos that followed the reign of Henry I and the loss at sea of his only legitimate heir, William Aethling.