David Cameron has accused Labour of viewing taxpayers as a "bottomless" source of cash as the Conservatives continued to try to place the economy at the centre of the general election contest.

The Prime Minister also told voters they had a responsibility to help cut Britain's budget deficit - by backing the Tories.

But he came under fire for excluding the NHS and immigration from the six major themes of his parties' election manifesto.

A new opinion poll, by ComRes for ITV, shows the health service had become the biggest issue for voters, closely followed by migration.

In an attempt to head off some of the criticism, Mr Cameron said yesterday (mon) that immigration would be addressed "very directly" as part of his party's campaign.

But following days of terrible headlines over pressure on health services north and south of the border, Labour leader Ed Miliband accused Mr Cameron of treating the NHS as the subject "that dare not speak its name".

Mr Miliband himself also came under pressure amid continued questions over whether or not he privately discussed using the NHS as a "weapon" in the election.

The Labour leader is accused of telling BBC executives that he planned to "weaponise" the issue and use it against the Conservatives.

Mr Cameron accused Mr Miliband of "wriggling like an eel" when asked about the issue at the weekend.

The Labour leader told the Andrew Marr Show on Sunday: "I don't recall exactly what I said, but what I'm clear about is we are in a fight for the NHS and I think that's really important."

In a speech in Nottingham, Mr Cameron set out his party's core message, that without the Conservatives the economy would founder.

Appearing under a banner proclaiming 'A Britain Living Within Its Means' the Prime Minister told supporters they had a "responsibility" to act.

"When you look at the children you love, do you want to land them with a legacy of huge debts?" he asked as he warned of "economic chaos" if anyone else except the Tories was in power in May.

He hit out at the opposition, saying that Labour would deliver either "higher taxes or general chaos".

He added: "You cannot treat the hardworking people of this country like a bottomless pit to be taxed and taxed again.

"The reason we have a deficit in this country isn't because we tax people too little, it's because we spend too much."

On the NHS, however, he confirmed Tory plans to increase spending, saying: "Not a penny will be cut from the NHS budget - instead it will carry on rising."

The Commons will today (tue) witness a bid by the Conservatives to show that Labour cannot be trusted on the economy.

MPs will be asked to vote on a new Charter for Budget Responsibility committing whoever is in government to eradicating the deficit over a three year period.

Labour has said it will back the plan - which it argues is compatible with its plans to erase the deficit "as soon as possible" in the next parliament.

But the Tories accuse the party of failing to set out what they say would be the £30 billion of savings required.

Labour has previously criticised Mr Osborne, who plans to balance the books by swingeing cuts to in-work benefits.

The Chancellor has accused Labour of planning to increase taxes by around 3p to make up for not matching his spending cuts.

But Ed Miliband has claimed those are figures plucked "out of the air" and said Labour would eliminate the deficit by spending cuts, tax rises on the rich and boosting the economy.

Mr Cameron also accused his Westminster rivals of "running away" from the TV debates - despite his own refusal to take part unless the Greens are represented.

Mr Miliband has said broadcasters should "empty-chair" Mr Cameron.

Former Tory chairman Lord Tebbit has warned voters will think Mr Cameron is "frit" if he misses the TV showdowns.