Britain's main opposition Labour Party Friday held onto a parliamentary seat in a by-election in marginal Peterborough constituency, but the newly established Brexit Party were not far behind.

It was the first assault on Westminster politics by the newly established Brexit Party, launched earlier this year by veteran Eurosceptic Nigel Farage.

Labour's Lisa Forbes polled 10,484 votes in the by-election, with Brexit Party candidate Mike Greene less than 700 behind, with 9,801 votes.

For decades the seat has see-sawed between Labour and the Conservatives, who came third in the by-election with 7,243 votes.

Labour's share of the vote fell 17 percent to 31 percent, just two points ahead of the Brexit Party. The Conservatives, who came second in the 2017 snap election, saw their share of the vote fall by 25 percent.

The by-election was called after the previous Member of Parliament, Labour's Fiona Onasanya, was sent to prison for lying over a motoring speeding offence.

It is the first time in British politics that an elected MP was fired by her own constituents through a recently installed procedure to allow local people to give local MPs their marching orders.

"Tonight's result is significant because it shows that the politics of division will never win," Forbes told her supporters after winning the election.

The by-election generated immense interest as it was a major test for Farage and his rookie Brexit Party.

The Conservatives and Labour will be clinically analysing the Peterborough result to gauge the likely impact in a general election.

According to a report of the Daily Telegraph, the Brexit Party claimed that it has 3,000 people prepared to fight for seats in a snap general election.

"We have shaken up British politics with none of the data that is necessary to win a parliamentary election. We've had two parties ruling for decades, that's not happening any more," said multimillionaire former Conservative supporter Greene, who had been tipped to win the by-election in Peterborough before the election.

The Guardian described the result as a setback for Farage's fledgling party. This was the first Westminster constituency it has tried to win since it was founded four months ago, the newspaper added.

The Brexit Party won a higher percentage of the votes than every other party in the European Parliament elections last month.