The former BBC director general Mark Thompson has accused the BBC Trust chairman Lord Patten of "fundamentally misleading" parliament over the extent of his knowledge of controversial six-figure payoffs to senior staff at the broadcaster.

Thompson alleges that Patten and the BBC Trustee Anthony Fry told "specific untruths and inaccuracies" in their evidence to MPs on the public accounts committee (PAC) on 10 July this year, in leaked evidence from the former director general sent to the same committee.

"The picture painted for the PAC by the BBC Trust witnesses on 10 July 2013 was – in addition to specific untruths and inaccuracies – fundamentally misleading about the extent of Trust knowledge and involvement," he writes. "The insinuation that they were kept in the dark by me or anyone else is false and is not supported by the evidence."

Thompson, who ran the BBC between 2004 and 2012, attacked his former boss in a detailed 25-page witness statement that will raises questions for Patten about his knowledge of two controversial severance payments.

Thompson provided evidence that he alleged showed Patten was wrong to tell MPs he "didn't know" about two critical aspects of settlements made with two departing executives, the £1m payout to former deputy director general Mark Byford in 2011 and the £390,000 settlement reached with Sharon Baylay, the former director of marketing. Thompson said that Patten knew in 2011 that both had received settlements of more than they were contractually entitled to, and their formal notice of departure was delayed.

"In fact, Lord Patten was himself fully briefed, in writing as well as orally, about the Mark Byford and Sharon Baylay settlements soon after his arrival as chairman in 2011," writes Thompson.

He goes on to accuse the BBC Trust of withholding key information from the National Audit Office's investigation into payoffs at the corporation. Thompson concludes that the evidence given to the NAO and the PAC on 10 July was "inadequate, and in some important instances, very misleading testimony".

The public spending watchdog revealed this year that the BBC paid £25m to 150 departing bosses between 2009 and 2012. This week after further scrutiny of the BBC accounts, the NAO said the broadcaster paid out a total of £2.9m in payments that went beyond contractual entitlement between 2006 and 2012.

"During the PAC hearing on 10 July 2013, the BBC Trust witnesses strove repeatedly to play down the significance of the two documents which had emerged at that time, and to make misleading and inaccurate statements, all of which served to minimise and draw attention away from the Trust's own knowledge and involvement," in the Byford and Baylay severance settlements, writes Thompson.

"The BBC Trust witnesses failed to mention the warning I had given them about misleading the PAC, or the extent to which they themselves had been briefed about these cases.

"Nor did they explain, given how much outrage they claimed to feel and how much they actually knew about the cases, why they did nothing about senior management severance until they themselves came under criticism for the payment made to [former BBC director general] George Entwistle."

On Monday, Thompson, Patten and Fry will appear before the PAC, chaired by Labour MP Margaret Hodge, in the latest hearing on excessive payouts.

MPs have been fiercely critical of both the BBC and the Trust over what they described as "corporate fraud and cronyism" among senior managers.

Speaking before details about Thompson's evidence to the committee had been made public, Hodge said she had seen evidence of "total chaos" at an organisation more concerned with its public image than licence fee payers' money.

Asked by BBC Radio 4's Media Show if she thought the committee had previously been misled, Hodge said: "We will have to discover that next Monday. Certainly those individuals we are having in front of us don't agree with each other on what happened or who knew what and until we can unravel that we won't know whether or not we were misled."

Also giving evidence on Monday will be former Trust chairman Sir Michael Lyons and Marcus Agius, the former chairman of the BBC Executive Board Remuneration Committee which was responsible for approving significant payoffs.

A BBC Trust spokesman said: "This is a bizarre document. We reject the suggestion that Lord Patten and Anthony Fry misled the PAC. We completely disagree with Mark Thompson's analysis, much of which is unsubstantiated, in particular the suggestion that Lord Patten was given a full and formal briefing on the exact terms of Mark Byford's departure, which in any event took place before the current Chairman's arrival at the Trust.

"It remains the case, as noted by the NAO in its original report, both that the Trust under the Chairmanship of Sir Michael Lyons was told that these payments were within contractual terms and that the Trust did not have a role in the approval process. The Trust has already published its own account of events, which took place well before Lord Patten's arrival, and we look forward to answering fully and openly further questions at Monday's PAC hearing. For Lord Patten and Anthony Fry the overriding concern remains the best interests and good standing of the BBC. "