Dirty hospitals are serving out-of-date food to patients, an investigation has found.
Meals are being prepared in mouldy kitchens, putting vulnerable patients at "high risk" of food poisoning, while others have unclean worktops, food trolleys and sinks.
The Press Association analysis of food hygiene reports obtained under the Freedom of Information Act and data from the Food Standards Agency (FSA), also revealed poor rankings for hundreds of care homes and children's nurseries.
Some 400 hospitals, hospices, care homes, nurseries and school clubs are currently listed as needing "major", "urgent" or "necessary" improvement. One care home was infested with cockroaches while another had evidence of rats.
The Food Hygiene Rating Scheme - which rates organisations and businesses from zero to five - is run by the FSA and councils in England, Wales and Northern Ireland.
Overall, eight health and care premises currently have a zero rating - urgent improvement necessary. None are hospitals.
Some 187 have a rating of one - major improvement necessary. Three of these are hospital premises, including the private Priory Hospital in Altrincham, Cheshire.
And 205 are ranked as two - improvement necessary. They include six hospitals and about 100 care homes.
Among those given the ranking of two was Glenfield Hospital in Leicester.
Problems were found in its kitchens serving patients, those in the Bennion Centre for the elderly, the Bradgate mental health unit and at the L'Eat restaurants for patients and visitors.
An inspection of patient catering kitchens in August found sliced chicken two days past its use-by date. Inspectors found staff had created their own date labels for when they thought food should be used, creating a "high risk" for patients who might develop food poisoning.
The experts also found leaking sinks, "inadequate" knowledge among staff about how to handle food safely, and mouldy areas, including the salad preparation room.
The report pointed to major problems with condensation, saying: "There was a lot of water in the corridors and store rooms caused by condensation on walls and ceilings which was dripping and pooling on the floor.
"There was a lot of mould and mouldy sealant caused by the damp conditions."
Flies were also found in the washing-up area, salad was being washed in a sink in direct contact with the plug and bags of salad had passed their use-by date but were being used for sandwiches and salads.
Food stored in freezers was not covered properly, with food having evidence of "freezer burn".
Inspectors also found dirty hand wash basins and food trolleys used to take meals to patients with "dried-on" food on them.
Other problems included rusty microwaves and staff not using disinfectant to clean worktops.
Furthermore, food was being kept in fridges with temperatures up to 13C despite rules saying they should be 5C or below to prevent bacteria developing.
At L'Eat, sandwiches and salads were being kept at 16C to 18C in display fridges. Mouldy red and green peppers were found in store cupboards, while beetroot, lettuce and tomatoes had all passed their use-by date.
Inspectors also found tin openers "encrusted with food", "dirty" containers full of "onion debris" being re-used, and badly damaged chopping boards.
The Bennion Centre report described mouldy kitchen areas and too-warm fridges with cheesecakes and tiramisu desserts way past their sell-by dates.
At the Bradgate unit, sandwiches were being kept at 15C to 21C, opened tins of tomato soup were found in the fridge, and dirty and worn scrubbing brushes were in use.
Darryn Kerr, director of facilities at Leicester's Hospitals, said the organisation was "disappointed" by the ratings. He said catering services were brought back in-house in May after being run by an external provider.
He added: "We take these matters very seriously and acknowledge the issues noted within the report. We already have an action plan in place to urgently address the areas that need improvement."
West Heath Hospital in Birmingham, which serves 42 inpatients and runs a restaurant, was ranked one in March.
Inspectors found dirt, out-of-date food, turkey and beef being frozen against instructions, with desserts and bacon being given too long use-by dates by staff.
A spokeswoman said operating procedures had now improved.
Parkview Residential Care Home in Bexleyheath, south-east London, was found to have an "infestation of Oriental cockroaches" during an August inspection.
The kitchen was closed voluntarily for the second time following a previous warning and inspectors gave it a zero rating.
Ivy House care home in Derby, which specialises in dementia care, scored zero after inspectors found evidence of rat activity. The home said the problems have now been rectified and related to an outbuilding.
Elsewhere, Hulton Care Home in Manchester was given a rating of one in August. Inspectors found raw meat being kept incorrectly and repairs needed.
A spokesman said it was awaiting a new rating, adding: "Following the inspection we worked with our catering partner Elior UK and quickly made the required improvements.
An FSA spokeswoman said: "An overwhelming majority, almost 99%, of hospitals and other care providers achieve a food hygiene rating of 3 - "generally satisfactory" - or better.
"The food safety officer from the local authority will be taking the necessary action to ensure that the issues identified at caring premises with a lower rating are addressed and that vulnerable people are not put at risk."