The UK Independence Party, led by the pub-clubbable Nigel Farage, has won a resounding second successive Parliamentary by-election and sent British politics tumbling into an abyss of the unknown.
Mark Reckless, the former Conservative politician who left the party for UKIP in September, won back his seat in Parliament Thursday in the Rochester and Strood by-election that was triggered by his defection.
UKIP is now more than just a fringe group thumbing its nose at the big parties: it is a wild card which can threaten all their prospects.
Few political experts would claim at this moment to be able to predict the outcome of the next General Election, which will take place on May 7, 2015. And nobody knows how many of the protest votes UKIP has been gathering will stay with them when voters are deciding who will govern the country.
But UKIP are still advancing: back in May, they won the European Parliamentary elections with 27 percent of the votes and 24 seats, the first time a party other than Labour or the Conservatives has done so.
What seems almost inevitable is that there will be another "hung" Parliament after the General Election -- meaning no party will win an outright majority of seats. But this time neither Conservatives nor Labour look like being able to build a coalition government without doing deals with more than one other political grouping.
Britain is likely to experience an unstable era of Scandinavian-style politics where the chief preoccupation of the political class is not solving the problems of the nation, but putting together deals to enable any decisions to be taken at all.
Reckless was the second former Tory to resign his seat and win his way back to Parliament in the purple colors of UKIP after Douglas Carswell had done the same in Clacton in October. And although his roughly 3,000 vote majority will be less sustainable at a General Election than Carswell's crushing victory, it keeps UKIP on track for its ambition of winning enough seats next May to hold the balance of power.
In Rochester, UKIP managed to resist a huge Conservative campaign that included five visits from Prime Minister David Cameron, who was desperate to stave off another UKIP victory that could call his effectiveness as the leader of the Tories into question.
UKIP also won over a significant proportion of the former working class Labour vote -- aided by a Labour front-bencher's online posting of a photo of a house in Rochester draped in English flags with a white van in the driveway. Politicians of all stripes were quick to pounce on Shadow Attorney General Emily Thornberry's ill-judged tweet as snobbish and derogatory, and Thornberry resigned her position before the night was over.
UKIP also reduced the Liberal Democrat vote to a derisory figure: some of their former protest votes on the Left are now going to the Green Party.
The UKIP bandwagon is still rolling. Reckless was a confused candidate who at one stage was slapped down by Nigel Farage for suggesting that EU immigrants might be sent home, but the party that secured a mere three percent at the last General Election in Britain has become a significant political player.
It is now the obvious receptacle for protest votes in the way that the Liberal Democrats used to be. But their participation in a coalition government with the Conservatives has shredded the Lib-Dems' political appeal.
UKIP has successfully harnessed to its bandwagon to the common feeling of disillusion with the two major parties and the Westminster "establishment." As well as its anti-European stance, it has profited from bringing immigration to the fore as a political issue.
This has spooked lawmakers in other parties who have demanded that their own party leaders must also get tougher on immigration -- a policy area on which few deal in facts but on which much emotion is expended. But the more that Labour and the Tories rush out new immigration policies, the more the public say: "We thought you told us that UKIP were a bunch of fruitcakes, but now you are agreeing they were right all along."
Political strategists used to believe that UKIP were chiefly a threat to the Conservatives, taking the votes of right-wing Euroskeptics away from them. But in the recent Heywood and Middleton by-election in the greater Manchester area UKIP came within a few hundred votes of grabbing a Labour seat too.
With the resurgent Scottish National Party threatening to grab 30 of Labour's 40 Scottish seats in the Westminster Parliament, and Labour's leader Ed Miliband proving the lowest-rated occupant of his position in polling history, Labour too are shivering at the UKIP intervention.
So where do we go from here? UKIP will revel in its triumph and redouble its efforts to entice more Euroskeptic Conservative MPs to jump ship in order to save their seats at the next election.
David Cameron, his authority badly dented after he promised to throw the kitchen sink at saving the Rochester seat, will be under massive pressure from his MPs to turn the political tide now with the major speech he has for some time been promising on immigration (and which he postponed for fear of having the Rochester result taken as a verdict on his efforts).
He is handicapped because the Conservatives' pledge to reduce immigration to less than 100,000 a year has failed because of the EU's commitment to the free movement of people within its borders, and German Chancellor Angela Merkel is heading Europe's refusal to reconsider that principle. That again plays into UKIP's hands.
Right-wing Euroskeptic Conservative MPs insist that their party and UKIP are part of the same political family, and they will now try to pressure Cameron into some sort of electoral pact -- arguing that otherwise Labour will "win" next May's election with less than a third of the votes.
Cameron will resist, but the irony for UKIP is that of all the possible election results, the only one that will bring about their chief political aim -- an in/out vote on Britain's membership in the European Union -- is victory for the Conservatives who have promised that referendum.
Robin Oakley was political editor and columnist for The Times newspaper in London from 1986 to 1992, the BBC's political editor from 1992 to 2000, and CNN's European Political Editor between 2000 and 2008. The opinions expressed in this commentary are solely his.