Liberal Democrat leader Nick Clegg has hailed his party's success in the Eastleigh by-election, telling activists in the Hampshire town: “We held our nerve, we stood our ground... we overcame the odds and we won a stunning victory.”
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 Prime Minister David Cameron was dealt a serious blow as the Conservatives were pushed into third place.
Visiting Eastleigh to congratulate his party's new MP, Mike Thornton, Mr Clegg said the message for Lib Dems from the poll was that “we can be in government and still win”.
Jubilant Lib Dem president Tim Farron said the result meant that 20-30 Tory seats were now vulnerable to the party in the 2015 general election.
But Conservative Education Secretary Michael Gove insisted that the party would not be blown off course by its defeat and would resist backbench calls for a shift to the right on issues like immigration and gay marriage.
“What we need to demonstrate is that the course that we have set is producing results,” Mr Gove told the BBC Radio 4 Today programme.
“If people think you are changing policy in order to take account of a by-election or to play party politics, that is when the problems arise and people think 'Do you know what? We smell inauthenticity here'.”
Mr Thornton 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, who said beating the Tories was a “humongous” shock which represented a “seismic shift” in UK politics.
Addressing cheering supporters at Hampshire Cricket Club's Ageas Bowl ground in the constituency, Mr Clegg said: "This has been a by-election we've had to fight in exceptionally difficult circumstances. Our opponents have thrown everything at us.
"We held our nerve, we stood our ground, we worked as a team, we went out and campaigned on every doorstep, we overcame the odds and won a stunning victory.
"In the past, I think people have sometimes made quite exaggerated claims about the political significance about individual by-elections, and of course I'll leave it up to the Labour and Conservative Parties to explain or seek to explain their very poor results last night.
"But for the Liberal Democrats, my view is the message is very simple: We can be a party of government and still win."
Mr Clegg said that when the Lib Dems entered coalition with the Tories, critics said they would "lose our soul, lose our values, lose our identity, lose our ability to win".
He added: "Last night we proved those critics are emphatically wrong."
Mr Clegg 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.
"That's what we proved last night and we proved it because we showed the people of Eastleigh... how we are delivering for them and their families, not just locally but nationally too."
Ukip leader Nigel Farage said success in the polls was not the result of a protest vote, but because his party connects with people who want it to speak for them.
He told ITV's Daybreak: "If people who have not voted for 20 or 30 years go out to the ballot box in a by-election and vote, that by definition cannot be a protest vote.
"It is people saying, 'Ukip, speak for me', and they are re-engaging with the democratic process. That is a long, long way away from a protest vote."
The Tories are wasting their time in working class towns and cities, he said, as they cannot connect with working-class voters because they are run by "as one of their own MPs said, a bunch of posh boys who don't know the price of milk".
Mr Farage said he didn't stand for election because he wants to lead the Ukip party as a candidate into the European elections next year, where he wants to cause "an earthquake" in British politics.
Asked if Ukip will have enough support by 2015 to repeat its success in Eastleigh, Mr Farage said: "Clearly, what we have got to do as a party, we have to get more members, we have to get certainly in some of the weaker parts of the country up above critical mass.
"But I don't see why after this result this party won't continue to grow.
"What is really exciting about this result is so often the media has said Ukip is sort of a gingerbread group, we pick votes up off the Tory party - what we did here last night in Eastleigh, a third of our vote came from the Conservatives, but two thirds of it came from the Labour party, the Liberal Democrats and from people who haven't voted for anybody for 20 or 30 years."