Nigel Farage has dismissed a welter of criticism over "racist" posters launching Ukip's campaign for the European and local elections.
The party leader said rivals were "screaming blue murder" over the images because they did not want to have an "honest conversation" about immigration.
The robust defence came after religious figures joined MPs in condemning the images, funded with £1.5 million from millionaire ex-Tory donor Paul Sykes.
It is Ukip's biggest ever publicity drive, as the party aims to achieve a political earthquake by topping the polls on May 22.
Cardinal Vincent Nichols, the leader of the Catholic Church in England and Wales, said it was wrong to use expressions that suggest "dismay or distress at all these people coming to this country".
Tory backbencher Nicholas Soames posted on Twitter: "At a time when our country really needs to come together, the Ukip advertising campaign is deeply divisive, offensive and ignorant."
Labour MP Keith Vaz, chairman of the Commons Home Affairs Select Committee, said: "Ukip have lowered the tone of the European debate with these spiteful and inaccurate claims on immigration which seek only to divide communities."
But Mr Farage told the BBC: "The fact that Westminster hate it and want to scream blue murder over it is because they have opened up the doors, they have fundamentally changed the lives of millions of people and they would rather we did not talk about it and just brush it under the carpet."
The Ukip posters, which are to be displayed at hundreds of billboard sites across the country, carry stark warnings that "British workers are hit hard by unlimited foreign labour".
Another says that 26 million people in Europe are looking for work, adding, with a picture of a finger pointing at the reader, "and whose job are they after?".
Under the slogan "Take back control of our country", others complain that 75% of British laws are made in Brussels and that UK taxpayers fund the "celebrity lifestyle" of EU bureaucrats.
Critics compared the immigration posters with those used in the past by the far-right British National Party, and Labour MP Mike Gapes said they were "racist" and appealed to "decent" voters to turn out to oppose Ukip.
Mr Farage said the party had known it was going to ruffle feathers among the "chattering classes".
He stressed that Ukip was not accusing foreigners of "stealing" jobs from Britons, but high levels of immigration from Europe had only been good for big business and rich people who wanted cheap nannies.
The poster campaign was highlighting the need to regain "control of our borders", he said.
Ukip says that its fast-rising membership has now passed 36,000 - only around 8,000 behind the Liberal Democrats and on course to overtake Nick Clegg's junior coalition party by the time of the 2015 general election.
Mr Clegg appealed for help from Labour and pro-EU Tories to counter Ukip's arguments in the run-up to May 22 and dismissed Mr Farage's claims to be an insurgent.
He wrote in The Guardian that Ukip is part of the anti-Brussels "establishment" and its leader is the sort of professional politician he accused others of being.
"Of all Nigel Farage's far-fetched claims - and there are many - the most outlandish is the idea that Ukip's call for an exit is the insurgents' battle cry," he said.
"What poppycock. For a start, Farage is every bit the professional politician he enthusiastically reviles. He and I were elected to the European Parliament on the same day in 1999. I left after five years. The Ukip leader is still there.
"More important, there is nothing remotely new about his party's ambitions. Ukip is simply the fresh face of a long-standing Eurosceptic establishment, supported by many in the Tory Party and significant parts of the press."
Mr Clegg acknowledged that a British exit from the EU was now "plausible" but insisted he would happily take on Mr Farage in more televised debates - despite being widely seen as having lost support to him after the two already broadcast.
Admitting that the pro-EU case lacked "volume", he said: "The Lib Dems have started this debate - but we cannot win it alone.
"We want to work with others to deliver the firepower needed to challenge the Eurosceptic establishment.
"If Labour is still a pro-European party, it needs to come off the fence. Tory modernisers must risk the wrath of their backbenchers and speak out."
Meanwhile, Poland's ambassador to the UK questioned the appetite of his countrymen any longer to seek work in the UK, saying wages were now higher in his country.
"This huge wave of people who came to EU countries trying to get well-paid jobs is over now," he told The Independent, 10 years after Poland joined the EU.
"There are more opportunities in Poland, we have had huge economic success, wages are higher in Poland now and there are more jobs in many parts of Poland, so I think this is over.
"We are getting out of the crisis and there are more and more opportunities in Poland. Of course people would like to stay in Poland and not live abroad. They love the UK but if you are at home there is no place like home."
Mr Farage told the Press Association: "I don't see how anybody can look at these posters and call them racist in any way at all.
"I know one Labour MP has come out and said it but that's classic of the type of Labour MP who's wanted to suppress debate on this question, brush it under the carpet and try and decry anybody who wants to discuss this as being racist.
"This, emphatically, is not a racist party."
Mr Farage was also asked whether he regarded himself as rich. "I'm not rich compared to the kind of people that run this country from Downing Street and the coalition leaders," he said.
"It's all relative but compared to them I'm pretty poor.
"The point is that wherever I come from, I did work for 20 years in the private sector and nine years running my own company. I've got some idea how this world works.
"I do feel increasingly we're run by a bunch of college kids who've never had a real job in their lives and don't understand that EU membership doesn't help business, doesn't help jobs, it's actually giving us a regulatory regime that's costing us business, costing us jobs."
Mr Farage said: "I did speculate yesterday that perhaps some of these images would get the chattering classes chattering.
"Well, they are chattering. In fact, they're outraged.
"They're outraged because we're actually telling the truth. There's nothing we're saying here that isn't true.
"And our euro-election campaign is to say to people: look, we're paying £55 million a day for the privilege of being in a club that now makes 75% of our laws and that gives complete open borders to 485 million people all of whom can come and work, live and settle in this country.
"And we're saying 'enough's enough' - we actually want to govern our own country, make our own laws, control our own borders and it's really interesting that 60% of ethnic minorities in Britain feel as strongly about the immigration issue as everybody else does.
"We cannot go on absorbing this many people with wage compression and youth unemployment having doubled."
Mr Farage went on: "These are the most important European elections that have ever been fought in this country. We've got a chance, four and a half weeks from now, of causing such a shock in the British political system that it will be nothing short of an earthquake.
"If Ukip win these elections, a referendum, an opportunity for us to get back control of our country will be one massive, massive step closer.
"And I actually think we are going to win these elections because I do think these messages resonate with people.
"We're not against anybody. We're not anti-European. We want a Europe of nation states that live together and trade together and that's why it's not just Ukip, there are other euro-sceptic parties doing well across the north of Europe."
Mr Sykes said he had "no idea" how much the campaign had cost him. "I haven't stopped spending yet. It'll be worth every penny," he said. "What do you think the freedom of this nation's worth? What do you think self-government of this nation's worth?
"I'm going to spend whatever it takes to make the British people aware that we're no longer governed from this great nation of ours."
Pressed on how much, he replied: "It's printed everywhere. You should have read the newspapers this morning. Apprximately, I don't know, 1.2 (million pounds), 1.4 (million pounds), who knows? There's many other people contributed, not just me."
Shadow international development secretary Jim Murphy told Sky News that Ukip's apparent support online was not necessarily all it appeared to be.
He said: "I think a lot of us in politics make a mistake of judging Twitter as the real world - it's not. Twitter is an enormous source for good, it can be a great place to get information, but it is also a place where an awful lot of people with very little else to do in their life camp for many hours of the day getting over excited.
"It happens here in Scotland, where you have a thing called cybernats who take to Twitter to insult anyone who wants to keep Scotland part of the United Kingdom, and I think to some degree Ukip have a similar group of people who are just so obsessive, so determined and so focused, they spend a lot of time on their phones or computers insulting and making accusations for no reason other than they disagree with them.
"I think there's a responsibility on us all in politics, regardless which side, to conduct ourselves with some degree of decorum and some degree of respect for each other's argument."
Mr Murphy said Mr Farage would make the Commons "more colourful", were he to be elected as an MP.
"I think he would possibly be seen in the House of Commons as an eccentric but I don't think that is going to happen," he said.