Labour finished fifth in the Henley by-election behind the Greens and BNP, and lost its deposit in one of the party’s worst electoral humiliations.

The seat, vacated by Boris Johnson, the new Mayor of London, was held by the Conservatives yesterday. David Cameron said that the emphatic win showed that his party was a credible alternative government.

The result was also a setback for the Liberal Democrats, who failed to make headway despite being in second place at the last general election and having had months to prepare.

Mr Brown, on a visit to Manchester to launch his new public service reform programme, said: “By-elections come and by-elections go.

“Of course, we have to listen to what people say. But my main job is to improve our public services, to get the economy moving forward, to make sure that in the health service and education people have the best services that they want and I am going to continue to do that. It is my job to make sure I can do more to help people’s standard of living improve.”

Mr Cameron said: “To have a further swing to Conservatives in such a strong Conservative seat, I really think is a very good result. It is obviously a disastrous result for the Labour Party, but I think I am right in saying it is the first time in a long time when there has been a contest between Conservatives and Liberal Democrats when there has been a swing to the Conservatives.

“I think what we are seeing is that people who voted for all sorts of different parties, including the Liberal Democrats, are now looking at the Conservatives and saying, ‘Yes, this is an alternative to the Government that I can believe in.’”

John Howell, the Conservative candidate, took the Oxfordshire seat by 10,116 votes. He received 19,796 votes; Stephen Kearney, for the Liberal Democrats, received 9,680. Richard McKenzie, for Labour, had 1,066 votes, behind the Greens with 1,321 votes, and the BNP with 1,243.

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