Labour and Tory members of the 11-man committee said if he had apologised, he would have been let off with a light reprimand, and his career would have been intact.
But it was a single word - "dissembled" - that sealed his fate.
When he read the report at 1.30pm in his office overlooking Whitehall in the Cabinet Office, he decided he had no option but to resign. He saw the Prime Minister at around 3pm. The ferocity of the report stunned MPs on all sides.
They queued at the vote office to get hold of the 60-page report. Within minutes, nearly 100 had been handed out. The "killer paragraph" - that in future the committee would take evidence on oath - was agreed at an early stage.
The Tories suggested that he should be charged with contempt of the House. Some Labour MPs suspected that it was put up to be knocked down, to let Mr Willetts off the hook. It was rejected on the ground that it was outside their remit.
But the fatal word "dissembled" was inserted at the end, on Monday night, in scenes of acrimony and high drama. Locked in disagreement in a committee room of the Commons, Labour MPs had suggested they should say they had found Mr Willetts's evidence to the committee unacceptable.
Quentin Davies, the Tory MP whose tenacious questioning of Mr Willetts in public session was blamed by ministers for inflicting the damage, suggested they should say they were concerned Mr Willetts should "dissemble" in his account.
Dissemble: v 1. conceal one's motives; talk or act hypocritically; 2. a/ disguise or conceal (a feeling, intention, act etc) b/ as dissembled adj.) simulated, pretended...
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