Cancer care in the NHS could be privatised for the first time in the health service's biggest ever outsourcing of services worth over £1.2bn.

A host of private healthcare firms have already expressed interest in securing a £689m, 10-year contract to provide cancer care at four NHS GP-led clinical commissioning group areas in Staffordshire.

The four CCGs involved, which care for 767,000 patients, are also seeking bidders for a separate £535m contract to provide end-of-life care. Together the contracts are worth £1.22bn, much more than the previous record high of £500m, secured by Richard Branson's Virgin Care for providing various health services in Surrey.

Virgin, Care UK, Ramsay Health and other private firms, many of which have increased their role in providing NHS care amid an expansion of competition driven by the coalition's NHS shake-up, have attended briefings run by the charity Macmillan Cancer Support, which is advising the four CCGs on the cancer contract.

Christina McAnea, head of health at the union Unison, expressed grave concerns about the plans. "This is by far the biggest procurement process in the NHS and is a dangerous experiment. We are talking about £1bn of taxpayers' money and contracts lasting 10 years in vital cancer services and end-of-life care," she said.

"CCGs are potentially handing over all decision-making on cancer and end-of-life care to private companies. This is much bigger than just asking private companies to provide a service: this is asking them to design the whole system. With profit as the main driving force, how can it not lead to problems?"

While an NHS organisation could bid for the contracts, the four CCGs said they were open to the successful bidder being an independent commercial organisation, third sector group or consortium.

The four CCGs – Cannock Chase, North Staffordshire, Stoke-on-Trent and Stafford and Surrounds – intend to overhaul cancer care in the county to make it more joined-up after some patients complained that they were "getting lost in the system, having to repeat themselves all the time, and that care [was] not always factoring in their personal circumstances".

Whoever wins the cancer contract will then have to "transform the provision of cancer care in Staffordshire and Stoke". The prime provider will "manage all the services along existing cancer care pathways" for the first two years after which "the provider will assume responsibility for the provision of cancer care, in expectation of streamlining the service model", according to details posted by the CCGs on the main NHS procurement website.

A new prime provider is needed to dramatically improve end-of-life care in Staffordshire because too many patients are not getting their wish to die at home, people needing palliative care are not being identified, and "patients and carers often report a negative experience, and their experience is of a fragmented, poor quality, unresponsive service", said the CCGs.

Concerns have been raised that handing the cancer contract to a non-NHS firm could lead to job losses at some of the 13 NHS hospital trusts that currently provide cancer care and the array of organisations that provide care to people who are dying.

The opening up to competition of such important high-value services has roused anger among opponents of the tendering of state-funded care. Paul Evans, director of the NHS Support Federation, said: "The most sensitive areas of NHS care are being opened to the private sector. This shows there is no limit to the willingness of the government to replace NHS services with those from profit-driven companies."

Andy Burnham, the shadow health secretary, said: "David Cameron and his ministers need to be reminded that they have never been given the permission of the public to put the NHS up for sale. Piece by piece, they are unpicking the NHS and selling it off to their friends in private health."

The row blew up as new evidence from the influential Nuffield Trust health think-tank showed that private firms have been becoming ever bigger providers of NHS care in England since the coalition took power in 2010. They increased their share of the NHS's £9.75bn annual spend on community health services from £1bn in 2010-11 to £1.77bn in 2012-13, up from 12% to 18% of the market. Similarly, private firms have experienced a 12% increase in their provision of mental health services over two years, from £1.05bn to £1.17bn, at a time when overall funding fell by 2.5%.

Andrew Donald, chief officer for Stafford and Surrounds and Cannock Chase CCGs, speaking on behalf of the quartet, said: "The Transforming Cancer and End of Life Care Programme is about taking an integrated approach to the commissioning and management of cancer, putting the patients at the centres of the process – it is not about privatisation."

The Department of Health indicated it was relaxed about what type of organisation secures the two contracts. A spokeswoman said: "The key thing is that patients get the best possible care, free at the point of use, no matter who provides it." She said NHS competition rules had not changed under the coalition government, but claimed "bureaucracy-busting reforms" were saving over £1bn a year.

Virgin Care is one of four bidders on a shortlist for a contract worth at least £800m to provide older people's services in Cambridgeshire and Peterborough, while another is a consortium comprising two NHS trusts and the firm Care UK.