Almost all of a central London hospital is to be sold and its services diverted to already stretched facilities around the capital under plans for NHS modernisation seen by the Guardian.

Charing Cross hospital, a flagship NHS facility in the heart of London, is to be cut to just 13% of its current size under proposals contained in sustainability and transformation plans published last year in 44 areas across England.

Many of the officially published plans lacked precise detail about how local services would change, but internal supporting documents seen by the Guardian reveal the scale of the closures at the London site.

The proposals claim much of the care currently offered at Charing Cross can be transferred to “community settings” such as local GP services, but health campaigners and clinicians say the transformation could endanger patients.

The documents include a map detailing how 13% of the current hospital site will remain, with the rest of its prime real estate in central London sold off. The plan is to introduce the changes after 2021.

NHS chiefs have stated as recently as March that “there have never been any plans to close Charing Cross hospital”, and in March 2015 the then prime minister, David Cameron, said it was “scaremongering” to suggest that the Charing Cross A&E departmentwas earmarked for closure. The health secretary, Jeremy Hunt, echoed the claims.

However, in the internal NHS documents the apparent downgrading of Charing Cross is outlined in great detail.

The plan is to axe 10 major services at Charing Cross – 24/7 A&E, emergency surgery, intensive care and a range of complex emergency and non-emergency medical and surgical treatments. The remaining services would be a series of outpatient and GP clinics, X-ray and CT scans, a pharmacy and an urgent care centre for “minor injuries and illnesses”. Around 300 acute beds will be lost.

The internal documents state: “The significant impact of reconfiguration on inpatient activity will be the movement of activity from Charing Cross and Ealing.”

Imperial College Healthcare Trust, which runs Charing Cross, stressed that the plans had not been taken forward since they were first drawn up because the hospital has seen the demand for patient care there continue to grow in the meantime”.

The plans have sparked a row between the borough where Charing Cross is based – Labour-controlled Hammersmith & Fulham council - and the NHS North West London Collaborative of Clinical Commissioning Groups, which is driving the changes.

Stephen Cowan, the leader of the council, has accused the NHS chiefs of deliberately misleading the public about the Charing Cross plans.

“It’s like demolishing someone’s house only to tell them they have in fact not lost their house – because they’ll be given a new garden shed which will be called their ‘local house’,” said Cowan.

He said NHS chiefs had rebranded the urgent care centre for minor injuries and would be run by GPs and nurse practitioners as a local A&E.

“That still constitutes the demolition and closure of Charing Cross hospital in its current form. No one would see what is left as a hospital in any generally accepted definition of the word,” Cowan added. “A ‘local hospital’ is a clinic. A class 3 A&E is an urgent care clinic.”

A spokeswoman for North West London Collaboration of Clinical Commissioning Groups said: “We are still committed to taking forward changes as agreed by the secretary of state in 2013. We have been clear that we will have local services in place to meet demand and deliver the necessary services for patients before we make any changes to Charing Cross.

“Our current focus is on delivering those new and improved services for local people. We have been clear that no changes will be made before 2021 and that for Charing Cross we will bring forward a strategic outline case in the future which sets out the capital requirement for making these changes and that remains our intention.

“As we look at changes to Charing Cross hospital we will of course continue to work closely with the council and value their important input into these discussions.”

A Department of Health spokesperson said: “The proposals in question are exactly that - proposals – and no final decisions have been made. As with all such cases across the NHS, decisions will be made after a public consultation and must have the full support of local doctors in order to secure the best outcomes for patients.”[NOTE: Three days following publication the Department of Health clarified that this statement did not specifically address the issue of the plans for Charing Cross hospital. The spokesman agreed that the comment from the Clinical Commissioning Group stated the true position and confirmed that these plans were consulted on and agreed in 2012/13, so the reconfiguration of those services is underway.]

NHS officials have accused Hammersmith & Fulham council of breaching the code of recommended practice on local authority publicity by circulating flyers to residents in March of this year warning of the closure of Charing Cross as a major hospital.

The council delayed replying due to election purdah but Cowan has recently drafted a response to NHS chiefs accusing them of “playing fast and loose with the English language” and demonstrating “a contempt for the public who you evidently hope are taken in by such misrepresentation”.

In the letter, Cowan adds that the published plans for the future of the hospital have avoided mentioning much of the detail contained in the confidential plans.

Charing Cross is thought to be one of five London hospitals that a recent government-commissioned review – by a former University College London hospital chief executive, Sir Robert Naylor – identified as each being worth more than £1bn if sold.

The NHS in England is gearing up to start selling off billions of pounds worth of land and property in order to free up cash to tackle what Naylor estimated to be a £10bn backlog of repairs to sometimes crumbling old buildings.

The Health Service Journal disclosed last week that the Department of Health was preparing to create six regional public/private partnerships covering all of England that would oversee such sales. The plan, codenamed Project Phoenix, would see the proceeds from asset sales being shared between NHS organisations and private firms. Under the plan, London and the south-east would comprise one giant, and very valuable, area.

• This article was amended on 20 June 2017 as a result of the Department of Health providing information which clarified its original statement.