LABOUR has renewed its challenge to David Cameron to face Ed Miliband in a head-to-head TV debate, after polls suggested that neither leader managed to secure a decisive lead in their first televised clash of the general election campaign.

An ICM poll for The Guardian found that the Prime Minister outperformed the Labour leader by a margin of 54%-46% in the Sky News/ Channel 4 Battle for Number 10 show, but a second survey by YouGov for The Times had a much closer result, with Cameron ahead by just 51%-49%.

The two men faced an aggressive grilling over their personalities and policies from veteran TV inquisitor Jeremy Paxman, as well as questions from a studio audience. But they did not debate one another directly, after Mr Cameron refused to take part in a head-to-head showdown with the man vying to replace him in 10 Downing Street.

Labour campaign chief Douglas Alexander urged the PM to reconsider his decision, telling the BBC: "We want as many of these debates as we can get. What we saw last night wasn't a debate. They were on the same stage, in front of the same audience, in the same building, but alas David Cameron wasn't willing to debate head-to-head with the alternative prime minister.

"Even at this late hour, with just six weeks to go, I challenge David Cameron again today - if you are half as confident as you pretend to be about your record in government, about your leadership, then let's put you in front of the British public next to the alternative prime minister for a job interview. With a week to go, let's have that head-to-head debate.

"I think this morning, it's a little clearer why David Cameron is so unwilling to have that debate."

But Conservative chairman Grant Shapps told the BBC: "Surely by now we should be on to discussing the issues at stake, rather than the format of these debates."

Mr Shapps said that the Conservative leader had shown he was "the man with the plan" in the Sky/Channel 4 broadcast, by spelling out how employment had risen under the coalition government and how Tories plan to eliminate the deficit without raising taxes.

"I know the broadcasters just want to carry on debating the five-year long debate from beforehand about the format of the debates," he said. "Let's actually talk about the serious issues here, let's talk about the detail of what was proposed.

"I thought on those grounds, David Cameron showed he had a competent programme for government. Ed Miliband showed that he would lead a chaotic government propped up by Alex Salmond and the SNP."

Mr Alexander said: "I believe that Ed Miliband began a process of reappraisal in the public's mind last night. He left behind a lot of the nonsense and caricatures you read in the newspapers.

"We welcome the opportunity - whether in the seven-way next Thursday or whether in the other programmes to take place in the next six weeks - to make our case to the British public, and then they will make the ultimate decision because they are the boss on May 7."

Scottish National Party leader Nicola Sturgeon said it was "hard to say" which leader had "won" the interviews, telling the BBC: "If you take some of the big key issues that people are really interested in, there was very little to choose.

"If you take austerity, we know that David Cameron wants to have deeper cuts in the next Parliament, but we also heard Ed Miliband say that he would have spending cuts as well, so there's no alternative there. On some of the key issues, it would have been very, very difficult to find much of substance that separated the two leaders."

Mr Cameron was put on the spot by Paxman over food banks and zero-hours contracts, and was forced to defend his relationships with sacked TV host Jeremy Clarkson and former HSBC boss Lord Green after the interviewer asked him: "What do you have in common with all these rich people?"

Meanwhile, the former Newsnight presenter told Mr Miliband that some of his MPs viewed him as a "liability", while he was seen as a "north London geek" by some voters, who thought "what a shame it's not his brother".

The Labour leader insisted he had the steel to be Prime Minister, saying he was "a pretty resilient guy" who had been "underestimated at every turn" and declaring: "Am I tough enough? Hell, yes, I'm tough enough."

Both took the opportunity to spell out core election messages - Mr Cameron promising to deliver a "strong economy", while his Labour rival insisted: "We can do a lot better than this. We're a great country." But there was little in the way of new policy and no killer blows dealt.

Mr Cameron said the UK was "immeasurably stronger" after five years of his premiership and claimed that "we've turned the economy round".

He defended his stewardship of the NHS, after an audience member accused him of breaking his promise not to impose a top-down reorganisation, telling her he had increased spending on health by £12.7 billion and recruited thousands of doctors and nurses while removing swathes of managers.

The Conservative leader told his audience in the studio and at home watching TV: "You are going to have to make this huge choice in 42 days' time. What I have learnt in the last five years is that nothing you want to do will work without a strong and growing economy.

"The schools we want for our children, the hospitals we want when we are ill. These things need that strong economy."

Mr Miliband said: "I think this is a choice between those who think this is as good as it gets for Britain and those who think we can do a lot better than this.

"The Prime Minister said he couldn't live on a zero hours contract, well I couldn't either, so let's do something about it."

Mr Miliband even won plaudits from Ukip leader Nigel Farage, who said he had won the personality battle. But his claim to have stood up to Rupert Murdoch prompted a withering response from the News Corp boss, who tweeted: "Thanks for two mentions, Ed Miliband. Only met once for all of 2 minutes when you embarrassed me with over the top flattery."

The Prime Minister was back in front of the cameras this morning as he visited a building site to promote the Help to Buy scheme.

Wearing a hard hat and hi-vis jacket, Mr Cameron did not take questions from the press as he toured the project in the Tory-held marginal Brentford and Isleworth seat in west London.

As he chatted to first-time buyers Alex Elias and Nivene El-Sidawi on the construction site of what will be their new flat, he asked "Where will the telly go?", but made no mention of his TV appearance last night.

Mr Miliband was asked to rate his performance as he took questions from reporters at Labour's general campaign launch at the Olympic Park, in east London.

He replied: "I will leave the sort of scores on the doors to other people. That's not what I am interested in.

"We were facing a tough fight yesterday and we're facing a tough fight today and what I valued about the debate last night was the chance to talk directly to the British people about the future of this country and how we change the country."