Labour has launched its general election campaign with a warning that the Conservatives would kill the NHS within five more years of government.

The party published its first campaign advertisement on Sunday showing an airbrushed David Cameron beside a slogan that warns he would mean longer waiting times, spending levels back to where they were in the 1930s, and more privatisation.

The decision of Labour to start the year with a “Save the NHS campaign” shows Ed Miliband’s party is planning to fight the election on the issue of health, while Cameron is trying to emphasise Conservative stewardship of the economy.

Both sides are wasting no time in getting their election campaigns under way in 2015. Cameron launched a poster urging voters to stay on track with the Conservatives for recovery on Friday, and told the Mail on Sunday that Labour’s plans would cost the country an extra £13bn – a claim hotly disputed by Miliband’s party.

The Labour Party (@UKLabour) Help us defend our NHS from the Tories: https://t.co/d3YxukhWE0 pic.twitter.com/6Cdv0Ibpl2

Miliband will give a major speech setting out his vision for the country under a Labour government. The party’s election chief Douglas Alexander released a 27-page dossier on Sunday listing Cameron’s “broken promises to protect the NHS”. It also set out new projections for what five more years of Conservative government would mean.

It claims seven out of the 15 patients’ rights enshrined in the NHS constitution have been breached. Labour said these included those setting maximum waiting times of four hours at A&E, 62 days for cancer treatment, and six weeks for diagnostic tests.

Alexander said a further five years of the Conservatives could lead to nearly 2m people waiting more than four hours in A&E, waiting lists reaching 4m and more than 20m patients waiting a week or more to see a GP.

“There is nothing which better symbolises the difference between Labour’s vision for the future and that of the Tories than our NHS,” the election chief and shadow foreign secretary said, in a memo to voters.

“We need your help to save it. Today we are launching a four-month campaign to make clear that our health service as you know it won’t survive another five years of David Cameron.

Facebook Twitter Pinterest David Cameron launches the Conservatives’ first election poster on Friday. Photograph: Christopher Furlong/Getty Images

“And another five years of this rotten government could put us on course for a doubling of the scale of privatisation as competition is put before patient care.

“That is why the NHS is on the ballot paper at this election. And that is why we will work morning, noon and night to save it.”

Labour’s plans for the NHS include creating a £2.5bn-a-year fund to pay for 20,000 more nurses, 8,000 more GPs and 5,000 more home care workers.

The Conservatives are disputing the claim of Labour’s new poster that under them public spending would return to the level of the 1930s. Tory sources said the Office for Budget Responsibility was clear that by 2019-20 spending on public services would be at its lowest level in real terms since 2002-03.

Speaking on the BBC’s Andrew Marr Show, Cameron said it was an absolutely key pledge of the Conservatives to protect the NHS but this could only be done if the economy was doing well.

He said he would like to “take the NHS out of politics” because it was such an extraordinary organisation. At the same time, he said the Conservatives would deal with some of the problems in the health service.