The leaders of the five "challenger" parties engaged in some heated exchanges as they fought to present their vision for Britain in a televised debate.

With coalition leaders David Cameron and Nick Clegg absent, Labour's Ed Miliband was the target of many of the attacks at from the other parties at Westminster's Central Hall.

Nicola Sturgeon and Nigel Farage both took aim at the would-be Prime Minister, with the SNP leader again offering a pact against the Conservatives and Farage accusing Miliband of "lying" about Ukip's plans for the NHS.

During the opening statements, Plaid Cymru leader Leanne Wood said her party would fight austerity and "work with progressives from other parties to deliver prosperity investment, job creation, public services and strong communities."

Farage then accused other parties of throwing spending promises around "like confetti" and said only Ukip could afford what it was offering, by cutting overseas aid and ending Britain's membership of the EU.

Nigel Farage was accused of attempting to 'exploit' people's fears. Credit: Stefan Rousseau/PA Wire

Miliband condemned David Cameron's "choice" not to debate and said Labour would "reject" the arguments of parties trying to break up the United Kingdom - taking aim in particular at Nicola Sturgeon.

Sturgeon, leader of the SNP, then said her party would "work constructively" with others in Westminster to deliver "progressive change for people across the UK".

But while Wood and Bennett echoed Sturgeon's desire to "keep the Tories out" of government, Miliband appeared unwilling to countenance a deal with any party aiming to "break up" the United Kingdom.

In one later exchange, Sturgeon urged Miliband not to "turn your back" on her offer, to which the Labour leader replied: "You want to gamble on getting rid of a Tory government."

Earlier, Farage and Miliband clashed over the NHS - with Miliband claiming the Ukip leader's plans to outlaw "health tourism" showed he sought to "exploit people's fears rather than address them".

Farage came back angrily shortly after, responding to a Miliband claim that Ukip wanted to privatise the NHS by saying: "You're lying to millions and millions of people and you keep on doing it."

Neither David Cameron nor Nick Clegg were involved in tonight's BBC debate. Credit: Jeff Overs/BBC/PA Wire

A snap poll by Survation for the Mirror immediately following the programme gave Miliband victory on 35%, followed by Sturgeon on 31% and Farage on 27%.

And while Nigel Farage prompted jeers from the audience after his claim that the BBC audience was overly left-wing, the absent David Cameron took perhaps the most criticism on the night - despite Conservative claims that he had not been invited.

As the debate got underway Sturgeon received one of the strongest crowd reactions of the night, claiming it was a "disgrace" that Cameron was not sharing the platform to "defend his record".

And afterward, Miliband put out one more challenge to Cameron, urging the Prime Minister to debate him one-to-one.