Gordon Brown has marked his first anniversary in No 10 with the humiliation of seeing Labour beaten into fifth place in the Henley-on-Thames by-election.
Labour candidate Richard McKenzie lost his deposit as he trailed in behind the Greens and the far right British National Party.
As expected, the Tory candidate John Howell comfortably held the seat with a majority of 10,116 over the Liberal Democrats, in a contest triggered by the departure of Boris Johnson to become London Mayor.
Tory leader David Cameron said the emphatic victory showed that voters of all political stripes now saw his party as an alternative Government which they can believe in.
While Labour had no hope whatsoever in winning in what is natural Conservative territory, party strategists will be alarmed at the dramatic collapse in its vote after it finished third in the last general election.
The result follows Labour's catastrophic loss of the Crewe and Nantwich by-election and its dismal showing in the local council elections and will only serve to deepen the mood of gloom in Downing Street.
Labour MP Martin Salter, who was put up to speak for the party after the count, said that they had been the victims of a classic third party "squeeze" although he admitted that he had not expected to do so badly.
"It is a grim result, our vote was squeezed just as every third party's vote is squeezed. I am very disappointed. We did hope to do better than that," he said.
"It is very difficult to divine a clear message for Gordon Brown in a seat in which we had no chance at all. It is one of the worst seats for Labour in the country."
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The Conservative candidate John Howell took the seat with 19,796 votes to the Liberal Democrat candidate Stephen Kearney's 9,680. Labour's Richard McKenzie could only poll 1,066 votes, behind the Green Party's Mark Stevenson on 1,321 and the BNP's Timothy Rait on 1,243.
