Nigel Farage has claimed Ukip would have won the Eastleigh by-election had the campaign been just one week longer, after a late surge saw the party leapfrog the Tories into second place.
He claimed that had the Lib Dems not been able to get a substantial number of postal votes in the bag ahead of polling day his candidate Diane James would now be the Ukip's first elected MP.
"It is my belief that without a doubt we won the vote on the day," he said. "We were not able to get to the postal voters in time and perhaps this is where we lost valuable support and where the Lib Dem campaign was on point.
He added: "One more week and I think it's fair to surmise that Ukip would have grabbed the first seat in Westminster."
However the Lib Dem's strongly deny the claim. "We won in postal votes and we won on the day," a spokesperson said.
Thornton who won the by-election - triggered by the resignation of disgraced ex-Cabinet minister Chris Huhne - with 13,342 votes, a majority of 1,771 over Ukip's Diane James.
Following Huhne's resignation, the Lib Dems moved quickly to hold the ballot, calculating the strength of their local party in Eastleigh and well-oiled by-election machine would be best suited to a short campaign.
MISSED CHANCE? Would Farage Have Won?
The Lib Dems held off a late surge by the UK Independence Party (Ukip) to win the by-election in the early hours of this morning, but the prime minister was dealt a serious blow as the Conservatives were pushed into third place.
Clegg said that last night's result "emphatically" proved wrong the critics who claimed that as a result of his decision to go into coalition with Tories in 2010, the Lib Dems would "lose our soul, lose our values, lose our identity, lose our ability to win".
"For the Liberal Democrats, my view is the message is very simple: we can be a party of government and still win," he said.
"My ambition has always been to lead our party from opposition into being a party of government, but not just that, into becoming a winning party of government."