The unprecedented appearance of the Prime Minister in a by-election was seen in the constituency as a last-minute attempt to swing the final wavering voters to Labour in a contest which is too close to call.
He dismissed the convention that Prime Ministers should not enter by- election campaigns. "I am the elected Prime Minister and it is my government that is seeking the approval of the people of Uxbridge on 31 July. That is why I want to visit the constituency myself to explain to local people why Uxbridge needs Andy Slaughter as their next Labour MP," he said.
Andrew Lansley, the Tory candidate's "minder" and a former head of the Conservative Party research department, said Mr Blair was making a mistake. "If they felt sure they were going to win, they would not bring him here, because it's a hostage to fortune for every future by-election.
"They will have to bring him in at every future by-election. I have sat in on discussions on whether the Prime Minister should go to by-elections ... and always you end up coming down to the same answer, which is no.
"If you lose, you put the Prime Minister on the line. If you win, you have committed the Prime Minister to going to every by-election."
Sir Edward Heath told local Tories that he had never visited a by-election when he was Prime Minister. The no-show convention also applied to Baroness Thatcher and John Major.
The by-election was caused by the death of Sir Michael Shersby, whose majority was slashed at the general election from 12,368 to 724.