The UK Independence Party has won its first seat in the UK parliament after Tory defector Douglas Carswell took the Clacton seat by a staggering 12,400 votes.
Mr Carswell claimed 60 per cent of the vote and said afterwards there was “nothing that we cannot achieve”.
In the night’s other by-election, UKIP came close to pulling off another shock.
Labour held on to Heywood and Middleton but UKIP slashed its majority to 617.
Conservative Party Chairman Grant Shapps said today the result in Clacton was a “wake-up call”.
It follows UKIP’s success in the last Euro elections.
There are now fears that a number of other Tory backbenchers, fearing that they may lose their seats at next year’s General Election may also defect to UKIP.
When Mr Carswell - a Tory MP since 2005 - switched party allegiance in August, he also resigned as an MP to trigger the by-election in the Essex seaside town.
In his acceptance speech he said: “I resigned from parliament to face this election because I answer first, foremost and last to you. You are my boss. I will not let you down.
“To my new party I offer these thoughts: humility when we win, modesty when we are proved right. If we speak with passion, let it always be tempered by compassion.”
Mr Carswell condemned the other Westminster parties for operating “cosy cartel politics”.
UKIP leader Nigel Farage said Mr Carswell was “a brave and honourable man”
He also addressed the party’s prospects on a wider front, saying “we must be a party for all Britain and all Britons: first and second generation as much as every other”.
“Our strength must lie in our breadth. If we stay true to that there is nothing that we cannot achieve. Nothing we cannot achieve in Essex and East Anglia, in England and the whole country beyond.”
For the Conservatives, Mr Shapps said that while UKIP were a threat to all the Westminster parties, they “cost Conservatives seats”, saying it put Labour leader Ed Miliband “one step closer to Downing Street”.
Michael Dugher, Labour’s vice-chairman, said his party would continue to “expose UKIP for what they are”.