Labour made clear its intention to ensure the NHS is a top election issue as the unofficial campaign ahead of May’s vote got underway.
The party said the health service could not survive a second term of Conservative government.
In a 27-page dossier published on Sunday, Labour said the current government had made it harder to see a GP, with one in four people now waiting a week or more for an appointment.
There are fewer GPs, it said, with the number of full-time equivalents falling from 62.4 per 100,000 population in 2009/10 to 60 today.
The party has committed to funding 8,000 more GPs and has set out a 48-hour appointment guarantee.
BMA chairman Dr Mark Porter said it was vital decisions on patient care were clinically - not politically - led, and essential the next government works in partnership with doctors.
He said: ‘We have repeatedly voiced our concerns that year-on-year reductions in real-terms NHS funding are continuing to threaten the quality of patient care and access to it. Equally, we believe that the changes to the NHS pursued by successive governments, such as increased privatisation and competition, are eroding the core principles of our healthcare system.
‘Instead of focusing on delivering high-quality care for patients, the NHS is being damaged by distracting reorganisation and increasing transaction costs.’
The NHS, he added, had reached a crossroads with pressure on services at a critical point with cracks beginning to appear including longer queues for GP services.
‘A doctor's primary duty is to their patient,' said Dr Porter. ‘It is vital that decisions around patient care are clinically not politically led. It is essential that the next government works in partnership with doctors to ensure the future development of the NHS and provide better co-ordinated care developed around patients’ needs.
‘The NHS needs more than party political promises to survive - it needs long-term, sustainable investment to ensure there are enough staff and resources to meet rising demand and provide the best quality care for our patients.’
Labour’s election chief Douglas Alexander said: ‘There is nothing which better symbolises the difference between Labour’s vision for the future and that of the Tories than our NHS.
‘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.
‘A Tory second term would put us on course for ever-longer waits for patients because they have no plan to give the NHS the cash it needs and want to take public spending back to 1930s levels.
‘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.’
David Cameron told the BBC’s Andrew Marr Show the Conservatives would protect the NHS and commit the funding required to protect the service. The NHS, he said, was ‘not unaffordable’.
The prime minister said he would like to ‘take the NHS out of politics’ because it was such an extraordinary organisation.
A Conservative spokesman said: 'We can only have a strong NHS by staying on the road to a stronger economy.
'Our long-term economic plan has meant we are able to increase the NHS budget in the next parliament to help fund Simon Stevens' Five Year Forward View. This plan will help meet growing demand, give the public better access to GPs and improve preventative care - and it is widely supported in the NHS.
'Ed Miliband has no economic plan and so would put the entire NHS at risk.'