Patients are being treated in cramped, unsuitable and badly laid out hospitals as ageing NHS buildings struggle to cope with the demands of the modern health service.
Nearly a fifth of facilities in use in England are deemed not up to scratch, according to data obtained by the BBC.
A host of major hospitals are among the worst affected along with mental health units and community hospitals.
Experts predict the situation will get worse due to cuts in building budgets.
The 2009-10 figures supplied by the Department of Health show 17% of the NHS estate which is occupied is deemed as "not functionally suitable for use".
This covers national standards for issues such as space, layout and design as well as the availability of toilets and storage space, and the suitability of office space.
To fall below the required standard, areas are deemed to need a major overhaul or complete rebuild.
Part of the problem relates to the age of buildings. Nearly a fifth of the NHS estate was built before the health service was formed in 1948 - there are even wards in buildings which date back to the 1700s.
Estate managers have also told the BBC money earmarked for building improvements has too often been diverted elsewhere.
Among the more serious problems identified are wards that are too small, poorly designed A&E units and services being spread across too wide an area.
There are 33 hospitals which have 50% or more of their estate classed as not good enough, while another 109 NHS sites - mainly mental health units and community hospitals - have problems on that scale as well.
The situation has shown signs of improving in recent years - mostly thanks to the investment in new hospitals through the private finance initiative - but the scale of the problem and prospects for the future are still causing concern.
Leading children's hospitals Alder Hey in Liverpool and London's Great Ormond Street have particular problems with space on wards.
Alder Hey has some wards less than half the size of what is needed for modern health care. The trust said staff and families were forced to deal with the "cramped and inconveniently laid out wards and a lack of privacy".
Meanwhile, a wing of Great Ormond Street has single rooms that are so small staff struggle to get all the equipment they need into them, while parents are forced to sleep in armchairs at times because they are not big to accommodate beds. The trust is looking to build new facilities, but is still £95m short in its fund-raising.
Nearly two thirds of the Royal National Orthopaedic Hospital in Middlesex is not up to scratch, the figures show. The areas include a sloping corridor which is so steep that electric vehicles are used to tow patients back on to wards after surgery.
Problems identified by other trusts include:
- A lack of wash basins for infection control purposes
- A&E units which do not have a separate children's section
- Too little single-sex accommodation
- A helipad sited on the other side of the hospital from the emergency department
- Key wards too far away from essential services such as operating theatres and scanning equipment
- Physio rooms that are too small and not appropriate for rehabilitation
While the problems are making services more difficult to deliver, all the trusts the BBC talked to said patients were not put at risk. Areas which are dangerous are closed down altogether.
Plans are being drawn up to improve some of the worst buildings, but there are fears the building projects could be scuppered because of the funding situation.
Keith Sammonds, managing director of the Healthcare Facilities Consortium, which represents estates staff, said unsuitable buildings made services "more difficult to deliver and require staff to work harder".
"My concern is that the situation is only going to get worse. Capital budgets are being squeezed and there is a lack of private finance available. It is distressing. Facilities and estates staff work really hard to do the best they can with the restricted resources available to them."
Katherine Murphy, of the Patients Association, added: "This chimes with what patients tell us about them being treated in cupboards because there is not enough space and seeing heart monitors lying next to dirty linen because there is nowhere to put them. It is chaotic and disorganised and does not help the healing process."
Peter Carter, general secretary of the Royal College of Nursing, said some of the old-fashioned facilities were simply "not suited for care in the 21st century".
But a Department of Health spokeswoman said it expected the NHS to address the problems.
"The situation in the NHS regarding functional suitability has improved, but making further improvements through better use of existing assets will be a fundamental part of the NHS drive to improve efficiency."