Nigel Farage has called the Prime Minister "Desperate Dave" over his suggestions that Ukip will not win any seats at the election.
The Ukip leader told the BBC's Andrew Marr Show that David Cameron has been "saying to these voters that have left him over the course of the last five years, 'Please come home'."
"They're not going back to a guy that's covered the country in windmills, that has slashed our armed forces, raised the level of the foreign aid budget ... those voters aren't going back," he added.
Ukip is the most-discussed political party on Facebook, with 15.6 million interactions during the election campaign to date and three million people talking about them.
With just six days to go, the social network will be lighting up the London Eye every night with information reflecting the conversations happening online.
The Conservatives came in as second most talked-about party on Facebook since the start of January with 12.2 million interactions from 2.5 million.
Labour had 9.7 million interactions, followed by the Liberal Democrats and the SNP - which both had two million - and the Green Party with 1.3 million. The DUP of Northern Ireland racked up 40,000, while Plaid Cymru had 31,000 and Sinn Fein had 4,000.
Facebook has said it expects politics to be the most-discussed topic on the social network this year.
Nigel Farage has said he regrets alleged anti-Semitic comments made by a Ukip general election candidate - and insisted his party was not racist.
Jack Sen, who was standing in West Lancashire, has been suspended after directing abuse at Labour candidate Luciana Berger.
Speaking to ITV News, Mr Farage said he was "sorry" about the comments, adding:
We've got over 5000 people standing for us at this election, and less than a handful have caused us a problem.
Ukip is a non-sectarian, non-racist party and we've actually got a remarkable number of people standing for us from every singel walk of life, from every religion and every ethnic group in this country.
A Ukip general election candidate has been suspended by the party over Twitter messages directed at a Jewish Labour shadow minister.
Jack Sen, who is standing in West Lancashire and describes himself on the site as "unapologetically politically incorrect pro-British", directed abuse at Luciana Berger.
"You're about authentic Labour as Ed Miliband. Protect child benefits? If you had it your way you'd send the £ to Poland/ Israel," he wrote in one message. In another, he said: "Britain's youngest Jewish MP, Luciana Berger, is facing criticism over her record of...." loyalties."
Ms Berger told Jewish News it was "clearly an anti-Semitic comment".
A Ukip spokesman said Mr Sen "has expressed views that in no way reflect the views of the party and any other of our hard-working dedicated candidates."
UKIP leader Nigel Farage said that his party is the only one to fight the SNP rather than appeasing it.
The only MPs in Westminster that will actually fight the SNP and not appease the SNP and demand that the English get a fair deal, and the Welsh too for that matter, are UKIP.
The BBC would lose funding and influence with Ukip in power, Nigel Farage said as he accused the broadcaster of bias.
It comes after the Ukip leader was not invited to take part in the main Question Time-style programme last night but did take part in an individual show broadcast separately in England and Wales.
Farage has now pulled out of a BBC Radio 1 appearance later today.
He told Sky News: "If I was in a position of power, I would take away a lot of the BBC's funding, a lot of their influence."
Ukip leader Nigel Farage has issued a staunch defence of his anger over the cost of treating foreign "health tourists" for HIV - claiming the support of a British sufferer for his stance.
The Ukip leader came under fire during a televised leaders' debate earlier in the campaign for suggesting the cost of their drugs should instead be spent on cancer drugs for deserving Brits.
At a special Question Time event, Mr Farage said Ukip could save "easily £1 billion" a year by prioritising NHS help on domestic patients.
"It's interesting. I have here a letter from a 30-year-old HIV positive man in London who says, why are the waiting rooms now full to overflowing? Why does it now take me three weeks to get an appointment," he told the audience.
"And he says to me, it is because since we opened the door in 2012 we're now incapable of providing HIV treatment for people legally living in Britain."
During the event, Mr Farage also claimed Britain could thrive outside the EU and vowed to push for a referendum before 2017.
And he rejected claims his party would become "redundant" if the UK voted to stay in the EU and claimed it could make party support stronger.
Mr Farage said: "If it's a full, free and fair referendum I will accept the result. Would it make UKIP redundant? No, because just look at what's happened in Scotland. The Scots – the Scots rejected their independence referendum and yet the SNP have gone to remarkable heights since then."
Ukip leader Nigel Farage has defended his stance on migrant workers, arguing "the cabbages didn't rot in the fields" before the UK opened its doors to Eastern Europe in 2004.
Speaking to ITV News after filming a Question Time-style programme, Mr Farage said migrant workers were only essential for "big business that wants cheap labour".
He added that he had no problem with using migrant workers where they were needed, but said he believed they should not be entitled to claim in-work benefits from day one.
Ask Nigel Farage will be shown on BBC One at 10:50pm tonight.
Ukip leader Nigel Farage has cancelled his question and answer session for BBC Newsbeat, the radio programme said.
Nigel Farage has cancelled his appearance in the Live Lounge for #Newsbeat tomorrow. We expect to hear from a UKIP representative next week.
It follows Ukip's request that police investigate the BBC over comments made during an episode of Have I Got News for You.
A Ukip spokesperson told ITV News Farage was not attending the event due to a "diary clash".
TV presenter Nick Hewer will join the panel on ITV's The Agenda this evening.
The Apprentice and Countdown star will debate with Ukip's first elected MP Douglas Carswell, Oranges Are Not The Only Fruit novelist Jeanette Winterson and Sunday Times columnist Camilla Cavendish.
Political Editor Tom Bradby hosts the show, which airs on ITV at 10.40pm.