London  - Grim news greeted Britain's Prime Minister Gordon Brown on his first anniversary in power Friday as his ruling Labour Party was pushed into fifth place in a by-election.

The Conservatives won the "safe" seat of Henley, near London, with a comfortable majority, which had become vacant after Boris Johnson gave it up when he was elected Mayor of London in May.

However, commentators expressed shock at Labour's slide, with figures showing that the party gained only 1,066 votes, positioned behind the Greens and even the racist British National Party.

Turnout in the by-election in the affluent constituency, best known from its annual rowing regatta, was just over 50 per cent, compared with nearly 68 per cent three years ago.

Commentators said the result showed that the electorate wanted to send a "message" to the Labour government that it was failing to address people's concerns over the economy.

The Liberal Democrats' national leader, Nick Clegg, said the result showed Brown's "days in Number 10 (Downing Street) are numbered." (dpa)