Britain's anti-European Union UK Independence Party (UKIP) won its second seat in parliament on Friday, in a by-election that could signal upheaval in a general election in six months' time.
Mark Reckless was re-elected to parliament with 42 percent of the vote, after defecting in September from Prime Minister David Cameron's Conservative Party to UKIP, which wants strict quotas on immigration.
Furious campaigning by the Conservatives to hold on to Rochester and Strood failed to beat back the UKIP advance and their candidate lagged behind on 35 percent, a blow to Cameron who had vowed to "throw everything" at Thursday's by-election battle and visited the constituency five times to campaign.
In his acceptance speech, Reckless made an appeal to all voters to make UKIP the kingmaker at the general election in May 2015, in the likely outcome of a hung parliament.
"Whatever constituency you live in, whatever your former party allegiance, think about what it would mean to have a bloc of UKIP MPs at Westminster large enough to hold the balance of power," Reckless said.
"If you believe that the world is bigger than Europe, if you believe in an independent Britain, then come with us and we will give you back your country."
It is the second seat snatched by UKIP after another Conservative defector, Douglas Carswell, won UKIP its first elected seat in the national parliament in a September by-election in Clacton.
Speculation over further defections to UKIP swirled after Reckless suggested two more Conservative lawmakers could switch -- an idea quickly dismissed by senior Conservative politicians.
Cameron has already promised a referendum on Britain's EU membership if his party wins next year's general election and has taken a harder stance on immigration in a bid to stem the flow towards UKIP.
Experts said the latest vote result could prove a key moment in the history of British politics.
"UKIP was not supposed to win this by-election," explained Matthew Goodwin, politics professor at Nottingham University.
The growing support for UKIP is likely to make it harder for either the centre-right Conservative party or the centre-left Labour party to win an outright majority in what is set to be closely-fought elections in May.
"All bets are off for the general election next year, literally anything could happen," said UKIP leader Nigel Farage.
But some commentators questioned whether Thursday's by-election might be a protest vote that could wane as the general election approaches.
"I think what you're broadly seeing is the voters using by-elections as a means of expressing their discontent at all the mainstream parties," said political commentator and columnist for the Daily Telegraph Dan Hodges.
"It's also important to remember that UKIP haven't in fact won a by-election: they've, if you like, appropriated seats via MPs who have crossed the floor from the Tories to UKIP."
The Conservative candidate for Rochester and Strood Kelly Tolhurst vowed to "fight every day until the 2015 election to return a Conservative to this constituency" after the result was announced.
National opinion polls show the Labour party slightly ahead of the Conservatives, each with roughly a third of the vote, and UKIP's support steadily rising to about 16 percent.
The by-election results showed both the Conservatives' junior coalition partner, the Liberal Democrats, and the opposition Labour party losing large chunks of support compared to the previous vote in 2010.
Reflecting anger at all main parties, seen as out of touch by many voters, the by-election also caused unexpected embarrassment for the Labour party.
Senior Labour lawmaker Emily Thornberry was forced to resign from the shadow cabinet after posting a Tweet seen as condescending towards working-class voters, showing a house festooned with English flags and the caption "Image from #Rochester".
"I've never been as uncertain this close to a general election how these things are going to play out," said Peter Kellner, president of pollster YouGov.
He added that the "core" UKIP vote was likely around 8 percent, made up of voters driven by a sense that Britain "has gone to the dogs".
"Immigration and to a lesser extent Europe are the scapegoats for a more fundamental problem. The typical hardcore UKIP voter wants to emigrate. But they want to emigrate to that other country called the past," Kellner said.