David Cameron is kicking off his campaign for No 10 with a pledge to deliver a "truly seven-days-a-week NHS" for England if the Conservatives are returned to power on May 7.

The Prime Minister will use a speech today to the Conservative spring conference in Manchester to set out plans for patients to be able to access hospital services at weekends as well as during the week.

The announcement comes the day after Ed Miliband launched Labour's campaign with his promise of a "double lock" to safeguard the future of the NHS with £2.5 billion of new investment and restrictions on further privatisation - underlining the importance of health as one of the key election battlegrounds.

Although health is a devolved matter, the battle over the NHS south of the border will have a major influence over who ultimately prevails in the General Election.

Mr Cameron will say that under the Conservative plans, hospitals across England will offer consultant-level services seven days a week by the end of the parliament in 2020.

"For years it's been too hard to access the NHS out of hours. But illness doesn't respect working hours. Heart attacks, major accidents, babies - these things don't just come from nine to five," he will say.

"And the truth is that you are actually more likely to die if you turn up at the hospital at the weekend. Some of the resources are not up and running. The key decision-makers aren't always there.

"With a future Conservative government, we would have a truly seven day NHS."

For Labour, shadow health secretary Andy Burnham said the Conservatives' plans lacked credibility.

"At the last election, David Cameron promised seven-day NHS services in his manifesto. Five years on, he's making the same promise again," he said.

"Not only has he failed to deliver on that promise, he made it harder for people to get a GP appointment from Monday to Friday. It is typical of the brass neck of a man who thinks he can take the public for mugs."