The UK Independence Party has made stunning electoral gains and declared itself the "official opposition" - largely at the expense of the Conservative Party and Liberal Democrats.
With UKIP averaging 26% of the vote so far in county council polls, leader Nigel Farage said he was "astonished" by the party's breakthrough, but put it down to what he described as the "total disconnect" between the "career politics" of Westminster and ordinary people on the streets.
"UKIP is actually speaking the language of millions of ordinary voters," he told Sky News' Boulton & Co programme.
It became the second largest party in Lincolnshire as the Conservatives lost control of that county council as well as Gloucestershire - and also reduced the Tories' grip on power in Essex and Hampshire.
The eurosceptic party also finished second with 24% of the vote behind Labour in the South Shields parliamentary by-election, triggered by the resignation of David Miliband, with the two coalition parties suffering a drubbing.
Mr Farage drinks a pint at the Marquis of Granby in Westminster
The new MP, Emma Lewell-Buck said her victory was a verdict on the Government's austerity measures.
It was another bad result for the Conservatives who finished third, and a disastrous one for the Liberal Democrats who lost their deposit and finished seventh with just 352 votes behind UKIP, the Tories, an independent, the Socialist Party and the BNP.
"Send in the clowns," said a jubilant Mr Farage, after UKIP candidates were famously dismissed by Prime Minister David Cameron as "fruitcakes, loonies and closet racists" and last week as a bunch of "clowns" by Tory Cabinet minister Ken Clarke.
"We've been abused by everybody, attacked by the entire establishment who did their best to stop ordinary decent people going out and voting UKIP, and they have done in big, big numbers," he told Sky News.
"By the end of today we are going to have a fair tally - and it sends a shock wave, I think, through the establishment."
Asked whether UKIP were no more than the beneficiaries of protest votes against the coalition Government, Mr Farage replied: "If you speak to the Westminster elite, they will tell you 'it is just a protest, nothing to worry about really'.
"When I meet UKIP voters they say, 'Nigel, we're voting for you because we believe in what you stand for'.
"These votes are not easily going to go back to the Labour and Conservative parties."
A UKIP spokesman said the party was on course to win "well over" 100 seats, with counting still to take place in the vast majority of English authorities and the Isle of Anglesey in Wales.
Labour's newest MP Emma Lewell-Buck wins the South Shields by-election
He said the council successes were a "stepping stone" to the party's eventual aim of winning parliamentary elections.
"If this is any sign at all, it will make a few MPs feel a bit less comfortable in their parliamentary seats," the spokesman added.
Senior politicians from the three main parties attempted to explain the UKIP surge, which could have major implications, particularly for David Cameron as he attempts to calm the fears of grassroots Tories nervous at the loss of votes to Mr Farage's party.
UKIP's success will heighten pressure on Mr Cameron to shore up right-wing support by legislating during this parliament for a referendum on EU membership.
Conservative Chairman Grant Shapps acknowledged that his party had been hit by the rise of UKIP.
He told Sky News: "We hear the message, we get it, we understand what people are saying. They want to see change faster in this country and that is what we intend to deliver over the next couple of years.
"We need to show that we are relentlessly on the side of hard-working people in this country, who want to get on in life, do the right thing, and Conservatives back them.
"We have actually been making progress - we've cut the deficit by a third and cut net immigration by a third.
"My main concern is to listen to the voters and make sure we are reflecting their concerns - putting jobs and prosperity and fixing the economy first and foremost - that's where all our time and energy is going to be focused."
Richard Elvin, the UKIP candidate who came second in South Shields
But the Tory grassroots and backbenchers were seething at the party's performance.
Conservative Party vice-chairman Michael Fabricant tweeted "life cannot go on as normal" for the main three parties "unless they have no ambition for 2015".
One defeated Tory councillor in Hampshire launched a scathing attack on Mr Cameron, saying: "I don't believe a word he says."
Alexis McEvoy lost her South Waterside seat to UKIP's Philip Fawkes - a retired headteacher and distant relation of gunpowder plotter Guy Fawkes, who won with a majority of 315 and a 37.2% share of the vote.
Mr Farage said the win showed "the blood of rebellion still runs in his veins".
Business Secretary Vince Cable conceded the results were "obviously very disappointing" for the Liberal Democrats.
He said voters had turned to UKIP as a protest over poor economic conditions and claimed the results emphasised problems in the Conservative party.
"Unfortunately this is part of the price you pay for being in government and I think the Conservatives have had an even worse night than we did, but, nonetheless, it's not great," he told Sky News.
In East Sussex, where Labour made gains, party leader Ed Miliband said: "I'm pleased with the gains that we made in Hastings and across the South, and indeed in other parts of the country, including Derbyshire and elsewhere."
More than 2,300 seats are being contested in polls for 34 English councils
Asked whether he was worried about the threat of UKIP, he replied: "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 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."
The Conservatives retained control in Buckinghamshire, Devon, Dorset, Essex, Hampshire, Hertfordshire, Shropshire, Wiltshire, West Sussex, Worcestershire and - narrowly - Somerset, where they lost five seats and the Liberal Democrats lost four.
But they were ousted from overall control in Gloucestershire, Lancashire, Warwickshire, Lincolnshire, Norfolk and East Sussex.
The Tories were sent a warning in their traditional Essex heartland, losing nine county council seats to a bullish UKIP.
And they were held to "Ransome" in Lincolnshire as mother-of-four Sue Ransome and her daughters Felicity and Elizabeth celebrated three UKIP gains in Boston.
Sushil Kantibhai Patel, the father of Tory MP Priti Patel - took second place behind the Conservatives as the UKIP candidate in the Bushey South ward in the Hertfordshire County poll.
There was some good news for Nick Clegg as the Lib Dems won the by-election in the Fulwood ward in the heart of his Sheffield Hallam constituency in South Yorkshire, ahead of Labour, the Tories and UKIP.
Labour gained Derbyshire County Council from no overall control - and won the mayor battle of North Tyneside with the party's Norma Redfearn ousting incumbent Tory Linda Arkley.
The BNP lost its only county council seat in Padiham and Burnley West in Lancashire.