Nigel Farage has hailed a remarkable night for Ukip in local council elections, which he said put them in with a chance of securing a seat at Westminster and had sent a "shockwave" through the political establishment.
With many votes still to be counted after Thursday's elections, Ukip have so far gained 42 county council seats in England and also claimed second place behind Labour in the South Shields parliamentary by-election, while the two coalition parties suffered a drubbing.
Nigel Farage celebrates a successful night for Ukip
Ukip became the second largest party in Lincolnshire, winning 16 seats and depriving Conservatives of overall control.
And the party - which won no councillors at all when the seats were last contested in 2009 - picked up 10 in Hampshire, nine in Essex, three in Gloucestershire, three in Somerset and one in Dorset.
Ukip has been derided by leading Conservative politicians who fear the party will split the traditional Tory vote - including Ken Clarke who described the eurosceptic party as "clowns".
After seeing his party make substantial advances in the elections, Farage told Sky News this morning: "Send in the clowns."
"We've been abused by everybody, attacked by the entire establishment, who did their best to stop ordinary decent people from going out and voting Ukip and they have done in big, big numbers," he said.
"At the end of today we are going to have a fair tally and it sends a shockwave, I think, through the establishment."
Challenged over whether Ukip were no more than the beneficiaries of protest votes against the coalition Government, Farage pointed out that his party has come second in five of the last six parliamentary by-elections, claiming: "This wave of protest certainly isn't short-term - it's lasting."
Describing Ukip as "numerically" the third party in British politics, he added: "I think if we get a by-election that comes up in the next few months that is not a safe Tory or Labour seat but is a marginal, we have every chance of winning it."
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 "shows that our potential with old Labour voters is very high indeed", said Mr Farage.
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.
Overnight counts took place at six authorities which were held by the Tories before the election, with Conservatives losing control of two.
As well as in Lincolnshire, they were ousted from overall control in Gloucestershire, where there were four gains for Labour and three for Ukip.
The Conservatives retained control in Dorset, Essex, Hampshire and - narrowly - Somerset, where they lost five seats and the Liberal Democrats lost four. With counting continuing in Hertfordshire, the Tories had already won enough seats to keep hold of the council.
Labour's Norma Redfearn ousted incumbent Tory Linda Arkley in the battle to be mayor of North Tyneside.
After the six overnight counts, the Tories had lost 74 seats and the Lib Dems were down 16. Ukip were the big winners with 42 gains, and Labour were up 26.
Initial results in Staffordshire, where counting will continue later, saw some Labour gains and the Tories losing their stranglehold on Tamworth.
Of the six Tory-held county council seats up for grabs in the borough, three fell to Labour and a fourth to an independent candidate.
Senior politicians from the three main parties attempted to explain the rise of Ukip, 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 Farage's party.
The prime minister is under pressure from within his party to enshrine in law before the 2015 election his commitment to hold an in/out referendum on the UK's membership of the European Union.
Cameron has promised the public a vote before the end of 2017 if he wins the next election, but London mayor Boris Johnson is among those calling for him to legislate for that commitment in this Parliament.
Conservative chairman Grant Shapps acknowledged that his party had been hit by the rise of Ukip.
"We have lost a lot of good councillors in the counts overnight," Shapps told ITV's Daybreak. "People have sent a message, we get it, we hear what people are saying, people are concerned that we get on with the big issues facing hard-working people in this country, like fixing the economy, sorting out the welfare system, helping hard-working people to get on.
"There is a lot more to do, there's two years to go until the next election and in the end it will be a choice between whether you want Ed Balls and Ed Miliband, for Labour, in Downing Street or David Cameron trying to make sure that this country is always a place where hard-working people can get on."
Labour's Hilary Benn said: "Ukip have clearly done very well. It's a party of protest and times are really tough. People are feeling the pain and some people are coming out who haven't voted before and expressing that by voting for Ukip."
Benn added: "It's a party of protest, I don't think it's a party of government."
With Labour winning two seats in Harlow, Benn said they had made gains in "the kind of places, the key seats in the South where we need to be making further progress".
Deputy Lib Dem leader Simon Hughes said the South Shields results showed Ukip "are now the protest party in certain seats where the rest of us are not within challenging distance".
But he said Labour was not picking up protest votes in the way an opposition party would expect.
"I think this is as worrying for Labour as for the Tories, but we will see," he told Daybreak.
He insisted the Lib Dems were doing well "in our territory" - areas where the party had MPs.
A Ukip spokesman predicted the party would receive more than one million votes, a higher level of support than at the last general election.
The spokesman said: "Where we are standing, we are taking an average of 26.2% of the vote.
"I can now predict with confidence that we will take more than one million votes - more than we took at the entire general election in 2010. It's likely that we might even reach 1.5 million."
The party is currently pinning its hopes of a Westminster seat on Portsmouth South, where Lib Dem Mike Hancock has come under pressure to stand down following a series of negative headlines.
But Farage acknowledged that its future success will depend on whether its warnings prove correct about the impact of Romanian and Bulgarian immigration once their nationals gain full rights to work in the UK at the end of this year.
"I think to a large extent what will determine Ukip's success next year and the year after is what happens with Romania and Bulgaria," he said. "We have put out the big warning that a lot of people are coming and it will lead to unemployment, and I'm afraid more crime in our cities."
Tory backbencher John Baron, who last month delivered a letter to David Cameron signed by 100 Conservative MPs calling for referendum legislation, said the results should be a "wake up call" for the Government.
He told the BBC Radio 4 Today programme the need for at least an attempt at legislation to reinforce the Prime Minister's referendum pledge was reinforced by the poll.
Mr Baron said: "I take the view Ukip are not simply a protest party. There are a lot of people in Ukip with genuine concerns.
"If you can deliver legislation in this Parliament, or at least show serious intent that if the Conservatives get in we will definitely have an in/out referendum in 2017, then my question to anyone is why would you bother voting for Ukip?"