Nigel Farage has warned the main parties he will "see them in Westminster" next year after Ukip scored significant victories in local elections.
With Labour, Tory and Liberal Democrat recriminations in full swing, Mr Farage insisted he was already focused on translating his surge to the general election - giving his strongest hint yet that he will stand in a Kent constituency.
He also stressed that he would keep highlighting concerns about immigration despite accusations of racism, arguing it will be an "even bigger" issue in the contest next May.
The combative words came as David Cameron, Ed Miliband and Nick Clegg counted the cost of a bruising night at the polls, with potentially more difficult European parliament results to come on Sunday night.
The Conservatives and Liberal Democrats have already lost hundreds of councillors as Ukip shouldered its way into "bellwether" parts of Essex like Basildon.
The Prime Minister dismissed calls from some backbenchers for a pact with Mr Farage, and conceded he needed to convince voters he had "answers" on the immigration
But Mr Miliband is facing the most serious questions after Labour failed to make the sort of gains to suggest he can get a parliamentary majority next year.
The party performed strongly in London, taking control of Hammersmith and Fulham, and had other notable successes including Cambridge and Crawley.
However, it did not secure key councils such as Swindon and was prevented from taking charge in its number two parliamentary target seat, Thurrock, by the Ukip advance.
Nerves have been heightened further by strong progress for Mr Farage in traditional Labour heartlands including Rotherham.
According to BBC projections with most councils declared, Labour did achieve the highest vote share with 31% - but their 2% advantage over the Conservatives would not be enough for outright victory in May.
Backbenchers Graham Stringer and David Lammy were among those breaking ranks to voice criticism of the leadership, after a difficult campaign that featured a number of perceived gaffes by Mr Miliband.
Mr Stringer condemned "unforgivably unprofessional" organisation, while former minister Mr Lammy accepted the party should have done better and warned that voters were "swallowing" Ukip's message on immigration and Europe. Ex-mayor of London Ken Livingstone suggested Labour had "woken up a bit late" to the threat from Ukip.
Mr Miliband dismissed criticism of the campaign and his personal performance, insisting there were deeper forces at work.
"I think in some parts of the country we've had discontent building up for decades about the way the country has been run and about the way our economy works and people feeling that the country just doesn't work for them," he said.
"And so what you are seeing in some parts of the country is people turning to Ukip as an expression of that discontent and that desire for change."
Mr Clegg also blamed a "very strong anti-politics feeling" among voters - making clear he would not be resigning to take responsibility for the collapse in his party's support.
Tories have taken charge of Kingston Council - the back yard of Energy Secretary Ed Davey - and the Lib Dems have lost control in Portsmouth amid Ukip gains.
"I certainly accept that there is a very strong anti-politics mood around, not only in our country but in many other parts of Europe as well. I think you will see that in European elections in the days to come," the Deputy Prime Minister said.
"There is a very strong mood of restlessness and dissatisfaction with mainstream politics and that is reflected in the results for all mainstream parties, including the Lib Dems."
Mr Clegg urged activists to highlight the policies the Lib Dems had brought to the Coalition, such as the pupil premium and raised income tax threshold.
"Where we do that, in those places where we are strong, we're still winning," he added.
More than 4,000 council seats at 161 English local authorities, including the London boroughs and those in Northern Ireland, were up for grabs yesterday. Votes were cast throughout the UK for the European Parliament contest to return 73 MEPs, but those results are not due until next week.
Labour had sought to play down expectations by suggesting a good haul would be increasing councillor numbers by 200, a mark they seem likely to achieve with a solid showing in London.
But academics had suggested they should be looking at more like 500 to be on course for a Westminster majority.
Labour sources argued that while it had been hit by Ukip outside the capital, the Conservative and Lib Dem vote had "basically collapsed into" Mr Farage's party.
Mr Farage said he expected Ukip to end up with "double" the 80 gains that many had suggested would be a good result - and predicted it would come top in the European elections.
Asked whether the party would widen its pitch to voters beyond an EU referendum and tighter immigration restrictions, Mr Farage insisted it already "clear principles" on cutting taxes and bringing back grammar schools.
He added: "Don't think the immigration issue is going to go away. I think the plight of the eurozone is such that immigration is likely to be an even bigger question at the time of the general election than it was last Thursday."
He confirmed he would be a candidate at the general election, saying he would be standing "south of the river" rather than in Essex. He has strong links to Kent, and is widely expected to run in either South Thanet or Folkestone.
Saying the "Ukip fox is in the Westminster hen house", Mr Farage added: "There are areas of the country where now we have got an imprint in local government.
"Under the first-past-the-post system we are serious players."
He went on: "We will see you at Westminster next year. This party is going to break through into the Westminster parliament next year."
Both Mr Farage and Mr Cameron rejected the idea of an electoral pact.
The premier said the Tory vote share was actually up on last year despite the impact of Ukip's aggressive attack on European Union membership and immigration levels.
"We are the Conservative party. We don't do pacts and deals. We are fighting all out for an all-out win at the next election," Mr Cameron said.
"People want us to deliver. The economy is growing, we are creating jobs, but we have got to work harder and we have got to really deliver on issues that are frustrating people and frustrating me, like welfare reform and immigration and making sure people really benefit from this recovery.
"We will be working flat out to demonstrate that we do have the answers to help hard working people."
He added: "I'm confident that in spite of the difficulties, this is a base from which we can go forward and win."
But Tory backbencher John Baron, MP for Basildon and Billericay, said Mr Cameron was still making mistakes and ceding ground to Ukip.
"Whilst accepting that Ukip is in part a protest vote, the political establishment has been too complacent over the EU. It must now heed the message from these elections," he said.
"No 10 must learn from past mistakes. First it tried to ignore, and then insult, Ukip. It then took our backbench campaigns to get a referendum, and then support for legislation.
"But even now mistakes are being made. We have immigration targets, yet cannot control the major EU component. We also need to make clearer that there will be no deal with Ukip.
"Labour and the Liberals need to wake up and support our commitment to an EU referendum. They have failed to deliver on past promises. Voters want their say, regardless of their views on EU membership."