British PM David Cameron today promised to "work really hard" to win back voters who abandoned the Conservatives for the UK Independence Party in yesterday's council elections.
Ukip gained at least 88 county councillors and secured second place in the South Shields parliamentary by-election, in a breakthrough result for the eurosceptic party which leader Nigel Farage claimed marked "a real sea-change in British politics".
After previously deriding Farage's party as "fruitcakes, loonies and closet racists", the Prime Minister adopted a notably less hostile tone in the wake of the results, insisting he would show "respect" for those who voted Ukip.
And he indicated he was ready to take tougher action on the cost of living, immigration and welfare in response to the concerns voiced by Ukip voters.
Mr Farage was revelling in the insults he has received from the mainstream parties, claiming that Tory Kenneth Clarke's dismissal of Ukip as "clowns" added three points to their share of the vote. As he toured TV and radio studios, the jubilant Ukip leader quipped: "Send in the clowns!"
With full results from 26 county councils in, Conservatives had lost 233 councillors and Liberal Democrats 75, while Labour gained 182, Ukip 88 and Greens two.
Conservatives lost overall control of Mr Cameron's home county Oxfordshire, as well as Cambridgeshire, the Isle of Wight, Norfolk, East Sussex, Lancashire, Warwickshire, Lincolnshire and Gloucestershire. Labour gained Derbyshire from no overall control, as the party bounced back from historic lows in 2009, when the seats were last contested, but failed to achieve the kind of advances that would suggest Ed Miliband was on the way to a landslide victory in the 2015 general election.
The South Shields contest, triggered by David Miliband's decision to quit as an MP, was won by Labour's Emma Lewell-Buck with a reduced majority of 6,505.
The 24% of the vote secured by Ukip's Richard Elvin to take second place led Mr Farage to declare that "our potential with old Labour voters is very high indeed".
But it was a bad result for the Conservatives, who finished third, and a humiliation for the Liberal Democrats.
Nick Clegg's party lost its deposit after securing just 352 votes, finishing in seventh position behind an independent, an independent socialist and the BNP.
Speaking in his Oxfordshire constituency, Mr Cameron said there were "major lessons" for all the mainstream parties.
"For the Conservatives, I understand why some people who have supported us before didn't support us again," he said. "They want us to do even more to work for hard-working people to sort out the issues they care about.
"More to help with the cost of living, more to turn the economy round, more to get immigration down, to sort out the welfare system. They will be our focus, they are our focus, but we have got to do more."
Asked if he stood by his "fruitcakes" attack on Ukip, Mr Cameron said: "Well, look, it is no good insulting a political party that people have chosen to vote for... We need to show respect for people who have taken the choice to support this party and we are going to work really hard to win them back."
Mr Farage said Ukip now has "every chance" of winning a House of Commons seat at the next by-election in a marginal constituency, which the party hopes will come at Portsmouth South this summer if beleaguered Lib Dem Mike Hancock is forced to stand down.
The Ukip leader told BBC News: "We have been abused by everybody, the entire establishment, and now they are shocked and stunned that we are getting over 25% of the vote everywhere we stand across the country.
"This is a real sea-change in British politics."
Mr Miliband travelled to Hastings in East Sussex, to celebrate three Labour gains in a southern constituency where the party must make inroads if it is to live up to his "One Nation" slogan.
Asked whether he was worried about the threat of Ukip, he said: "In a way, part of Labour's challenge at the next election campaign is not the Tories, or the Lib Dems or even Ukip, it's the idea that nobody can really change the country, and that mainstream parties can't change the country.
"I believe Labour can change the country. I believe we have convinced a lot of people of that in these elections and that's why we have made a lot of gains, but I also know that there's work to do that goes on."
Lib Dem president Tim Farron acknowledged the result in South Shields was "shocking" for his party, but insisted it did not represent the whole picture.
He told the BBC Radio 4 Today programme: "The Westminster battlegrounds are where it is at and for the Lib Dems, South Shields is one extreme where we have got little strength on the ground and have been obliterated, and then you look at other places like Cheltenham, Taunton, Eastbourne, hopefully west London, places like West Dorset where we have got to win at the next election where we are doing extremely well.
"Most of our battles are against the Tories and against the Tories we are doing very well."
Ukip's successes heaped further pressure on Mr Cameron to shift to the right on issues like Europe, immigration and gay marriage.
Tory backbencher John Baron, who has written to the PM urging him to legislate in this Parliament for a referendum on EU membership after the election, said that the party leadership must now learn from its "errors" in handling the Ukip threat.
"Our commitment to an EU referendum needs to be believable," said Mr Baron.
"David Cameron should therefore heed the advice of the 100 Conservative backbenchers who signed my letter, and support legislation in this Parliament for a referendum in the next. This would show serious intent. Why, then, bother voting Ukip?"
Tory former Cabinet minister John Redwood said the results showed that voters, like Conservative MPs, "want faster progress on the new relationship with the EU".
But Education Secretary Michael Gove dismissed speculation over a Tory leadership challenge as "bonkeroony".
"It's barmy, the idea of changing the leader is bonkeroony," he told BBC Radio 4's World At One.
Mr Gove insisted the "course is clear" for voters who want a referendum on Europe - "They should campaign as energetically as they can for a Conservative victory at the next general election."
Mr Miliband enjoyed a major boost as Labour seized control of Nottinghamshire from the Conservatives.
Labour picked up 18 councillors, while the Tories lost 14, Independents two and the Lib Dems and Ukip one apiece, giving Mr Miliband's party a one-seat overall majority on the county council.
With full results in from 29 councils, Labour had gained 214 councillors, Ukip 103 and the Greens two, with the Tories losing 263 and the Lib Dems 90.
Outspoken MP Nadine Dorries - who is currently suspended from the Conservative whip - said today's results heralded the beginning of a "four-party system" and predicted further gains for Ukip.
She said the "political landscape has changed significantly" and that her party needed to change to avoid "losing badly" at the next general election.
Ms Dorries told BBC News: "A year ago I predicted on television and on the radio that if we continued as a Coalition pursuing the policies that we were, and continuing in that vein, that we would do badly today, that Ukip would probably become the first party in the Euro-elections next year, and that we would lose badly in 2015.
"The Prime Minister and the entire party is at liberty to ignore my predictions but I think today they can no longer ignore what people in the street are saying, and what they are saying is they don't like what we're doing and we have to change.
"If we don't, Ukip will do much better than they have to date going forward."