Miliband and Farage clash on cuts
The leaders of the five main opposition parties are going head-to-head in front of a live television audience at the BBC "challengers" debate.
The first clash of the evening came between Ed Miliband and Nigel Farage with the Labour leader saying that Ukip's sums for clearing the deficit "don't add up".
"You have got to make a judgment in this debate about balance and fairness," he said.
"Nigel actually wants to cut the top rate of income tax even further for the highest earners in our country - another £43,000 tax cut. I just have a different view about the way our country succeeds."
Mr Farage hit back: "Our sums do add up. You obviously haven't read the manifesto. You should. We have proposed tax cuts for the rich. This is not the right time to do that."
He added: "This year we are borrowing £90 billion more, our debt is £1.5 trillion, we have a real problem here and I have not heard from you Ed a single cut that you would make, not one."
He said that Ukip's plans to leave Europe would be a "disaster" for jobs in the UK.
"The reality is that for the NHS and education, Nigel, your plans - they are like David Cameron's plans and they are dangerous for our core public services," he said
Both the Scottish National Party's Nicola Sturgeon and Plaid Cymru's Leanne Wood denounced the Conservative proposal to extend the right to buy to housing association tenants.
Ms Sturgeon described the policy as "one of the worst ideas I have ever heard" and insisted Right to Buy was "a policy that has had its day", while Ms Wood said the Tory proposal was "one of the worst policies I can think of if you are thinking about reducing homelessness - this will increase levels of homelessness and that's not on".
Mr Miliband said he was not opposed to Right to Buy in principle, but added: "I don't thing the Tory plan works because there is no money for it. All it will mean is the social housing stock being watered down and fewer homes to rent."
But Ukip leader Nigel Farage said other leaders showed "a remarkable lack of comprehension" of the laws of supply and demand in housing, arguing: "A rapid rise in population due to open door immigration ... has directly contributed to the housing crisis.
"If you have net migration running at 300,000 a year, that's 300,000 people who need somewhere to live."
Mr Farage risked alienating the audience in Westminster's Central Hall, as he protested they were "a remarkable audience even by the left-wing standards of the BBC" after some of his comments about pressure on housing due to immigration were greeted with mutters.
Presenter David Dimbleby intervened to say: "This audience was carefully chosen by an independent polling organisation to represent the balance between all parties."
And Mr Miliband gave the Ukip leader the advice: "It's never a good idea to attack the audience."
Mr Farage retorted: "The real audience are sitting at home."
Ms Sturgeon won loud applause as she urged Mr Farage to "put the bogeyman to one side", telling him: "We have a housing crisis across this country. You know what, Nigel Farage? It isn't caused by immigrants. In your world every problem is caused by immigrants."
Green leader Natalie Bennett said: "We have had a market-led housing policy over the last decade or more that hasn't delivered homes. That's why we need to build homes for social rent."
Mr Miliband told Mr Farage that quitting the EU would be "a disaster for our country, a disaster for jobs, a disaster for our economy".
During debate on immigration, Mr Farage was accused by Ms Bennett of "demonising" migrants and by Ms Sturgeon of "intolerance".
The Ukip leader responded: "When you lose an argument in politics, you tend to start abusing your opponent, and we've seen quite a lot of that recently."
Ms Bennett said: "There is someone here on this platform who wants to utterly demonise migrants. I want to celebrate the contribution of migrants to Britain and I believe we all should doing that."
Ms Sturgeon said "strong" controls on immigration were needed, but added: "Let's not duck the issues, but let's make it civilised and not have it driven by the intolerance of Nigel Farage and his colleagues."
Ms Wood told the Ukip leader: "You abuse immigrants and those with HIV, and then complain that you get abuse."
But Mr Farage insisted that Britain was "not in a position to cope" with the scale of immigration and that Ukip's favoured Australian-style points system for migrants would be "a fair, ethical policy and it would work".
Mr Miliband said it was important to accept that "people's concerns are not based no prejudice, people's concerns are real and we have to address them."
In response to a question of the renewal of the Trident nuclear deterrent, Mr Miliband and Mr Farage said they supported it while Ms Sturgeon, Ms Wood and Ms Bennett were against.
"If it comes to a choice on how to spend £100 billion I choose childcare, health and education over new Trident weapons any day of the week," Ms Sturgeon said.
Mr Miliband said that the unpredictability of future threats meant that it was right to retain Trident although he said that Britain needed to be prepared to take a more independent line from the US on foreign policy.
"Britain's national interest will often coincide with America's but not always. You need a prime minister who is willing to say 'no' when it's appropriate and that's what I'll do," he said.
He was however challenged by Mr Farage over a call by European Commission president Jean-Claude Juncker for the creation of a European army.
"We now have the bosses of the European Union, including the French president, saying they want to build a European army.
"You can shake your head all you like but this is happening. If it did come to a European army would that be enough for you to give people a referendum," he demanded
Mr Miliband retorted: "I'm not going to have a European army."
But he said that the rise of Islamic State (Isis or IS) showed that Britain could not withdraw from the world "otherwise those problems will visit us here at home".
He was challenged by Ms Wood, who said: "Do you really think the problems caused by Isis can be resolved by nuclear weapons. If you were prime minister would you press the button?"
Mr Miliband replied: "No, it's not about Isis."
Ms Sturgeon condemned the "disgraceful" Tory attack on Mr Miliband which accused him of being prepared to "stab the UK in the back" over Trident in order to do a deal with the SNP.
She added: "Ed and I don't agree on Trident although I think some of his members agree with me on Trident."
Mr Farage said that the prospect of a Labour government propped up by the SNP was "very concerning for English voters who are worried about the Scottish tail wagging the English dog".
The Ukip leader said he could have done a deal to support a Labour minority administration if they had accepted an in/out referendum on the UK's EU membership.
"Ukip could have worked with a Labour Party that believed in the British people having a say on the greatest constitutional question of the day," said Mr Farage.
"They have turned their back on it. If they had offered a referendum, we could have worked with them, but they turned their backs on the British people."
The Ukip leader said that "the only issue" was Britain regained control of its own country and said his party's role if Tories win the election will be to ensure that any referendum is "an honest one, not a stitch-up".