Chancellor Gordon Brown has allowed a dentist to drill through to deep nerve tissue beneath his teeth without using an anaesthetic.
Mr Brown was said to have been stoical throughout
Mr Brown made the apparently painful decision because he did not want his mouth to freeze up just hours before he was due to deliver a speech.
The root canal work was carried out by Mervyn Druain of Belsize Park, London.
He told The Sun newspaper that Mr Brown had been "perfectly relaxed" and "did not flinch or grimace at any stage".
The chancellor spoke three hours later on the issue of citizenship training for migrants.
The operation on Mr Brown, the favourite to succeed Tony Blair as prime minister, will remind some seasoned cinema-goers of a gory scene in the 1976 hit film Marathon Man.
Mr Brown spoke a few hours later
In it, Sir Laurence Olivier, playing Nazi war criminal Dr Christian Szell, tortures a character played by Dustin Hoffman by carrying out excruciating dental surgery without an anaesthetic.
But a spokesman for the British Dental Association said Mr Brown's experience was unlikely to have been as gruesome.
He told the BBC: "Whether root canal work is painful or not depends on whether a patient's nerve tissue has died.
"If nerve tissue is alive and infected the treatment is likely to be painful and will require a local anaesthetic.
"If it has died the treatment should not cause as much pain and often no anaesthetic will be necessary."
He is not the first chancellor and would-be prime minister to have had high profile dental work.
John Major had to have an impacted wisdom tooth removed in 1990, shortly before the Conservative Party elected him its new leader in succession to Margaret Thatcher.
It is believed this operation involved anaesthetic.