The Department of Health has quietly doubled the amount of land it intends to dispose of, triggering accusations of desperate measures to plug a big hole in NHS finances.

Details of more than half of the 1,300 hectares now up for sale have been kept under wraps because of “sensitivity” – raising suspicions that many other sites also have clinical uses.

Today’s analysis, carried out for Labour by the House of Commons Library, went through Department of Health data of land that NHS organisations “have deemed surplus” and eligible for sale.

Of the 543 plots, totaling 1,332 hectares – worth many hundreds of millions of pounds – 117 are currently being used for clinical or medical purposes, Labour said.

However, data on 734 of those hectares, spread over 63 sites, has been held back due to “issues of sensitivity”, the analysis found.

Jonathan Ashworth, Labour’s Shadow Health Secretary, claimed a long-running failure to fund the NHS properly had forced “a blanket sell-off of sites which are currently being used for patient care”.

“Crumbling hospitals are in desperate need of investment for repair and renewal,” Mr Ashworth said.

“But the Government must provide that investment, not strip hospitals of their assets and force them into a fire sale.

“There has been a huge rise in the amount of NHS land available for sale this year, but for more than half of it the Government are keeping the details secret and refusing to fully answer reasonable questions.

“It all adds to the suspicion that ministers are drawing up secret plans for a fire sale of valuable NHS assets to plug the black hole in their finances.”

The criticism comes as Labour launches a major assault on the Prime Minister’s management of the NHS, warning her tenure has seen rising waiting times, cancelled operations and a growing crisis in social care.

However, the Department of Health hit back, insisting only truly unwanted land would be sold – with the cash raised ring-fenced to improve NHS services.

“There will be no ‘fire sale’ of NHS assets, but we continue with our ongoing efforts to help hospitals dispose of land they do not need,” a spokesman said.

“This will provide vital funds for the NHS to spend on patient care and free-up space for much needed homes.”

Ms May’s adoption of the Naylor report triggered criticism during the campaign. Dr Kailash Chand, the former deputy chairman of the British Medical Association, called it “an outline to sell off the NHS”.

The NHS Confederation then urged the Government to step back, calling for the land to be set aside for homes for NHS staff unable to buy on the open market, because of the housing crisis.

It linked the housing shortage to rising NHS vacancies, with 15 per cent of registered nursing jobs unfilled and 12 per cent of positions at GP practices vacant.

The most valuable site on today’s surplus list is the Royal National Orthopaedic Hospital, in Stanmore, London, which has a market value of £38.75m.

Other highly-priced locations include the Ida Darwin Hospital, in Cambridge (£20m), two sites at Broadmoor Hospital, in Berkshire (£16.75m and £11m), the Royal National Hospital for Rheumatic Diseases, in Bath (£10m) and Papworth Hospital, in Cambridgeshire (also £10m).

Meanwhile, Jeremy Corbyn, on a visit to Cornwall, will focus on the condition of the NHS to mark the release of performance data up to the point of the Prime Minister’s first anniversary in No 10.

He will say that, after 11 months, nearly 2.4 million people had waited more than four hours for treatment in casualty departments – or one in 10 patients.