Mr Dimbleby deliberately adopted glasses and a short haircut to give himself a headmasterly manner to conduct his most aggressive interview, according to experts in the black arts of television interviewing.
"That was the toughest David Dimbleby has ever been," said Des Wilson, former Liberal Democrat spin doctor.
"You got the feeling that the BBC thinks Blair has given few big interviews and may have ducked out of the debate, so they were determined to make sure they put him to the test."
Mr Wilson claims Mr Dimbleby's attitude was apparent in his remark that Mr Blair was "relatively young". "He was like the headmaster with the insubordinate prefect right from the starting gun," he said.
Westminster insiders have speculated that Mr Dimbleby has been stung by comparisons with the popular and aggressive Newsnight presenter, Jeremy Paxman, and Today's John Humphrys, and has adopted a more aggressive interviewing technique. The BBC denies there has been a change of style.
Mr Wilson believes Mr Dimbleby is a tougher interviewer than he is generally given credit for. "Because he is mild mannered and doesn't sneer at you, Dimbleby doesn't attract attention, but he is very sharp.
"But by dragging up his record from 10 or 12 years ago, he played into Blair's hands. Blair could then turn it into a list of how much Labour has changed. A Panorama spokesman, John Steel, said: "Some of the calls to the duty officer claimed that we were too soft on him, that it was a party political broadcast for Labour, so we cannot win."
"Politicians receive considerable media training and coaching and are adept at not answering questions they don't want to answer. So we need to find equally effective ways of making sure they do answer."
Michael Barratt, the former presenter of Nationwide who runs a media training agency for businessmen, said: "You give someone media training to get them to tell the truth and get their message across. But then I don't train politicians."