Filthy NHS wards are being plagued by pests - with maggots found in slippers and rats in maternity units, it was revealed last night.

Hospitals are so dirty that pest controllers were called out to 20,000 infestations in the past two years.

Experts warned that the appalling levels of hygiene added to the danger to patients from the deadly superbugs MRSA and C.diff, which multiply in the same environments as pests.

Health of the nation: Dirty mops propped up next to a filthy food trolley in an NHS hospital

Official figures obtained by the Tories show that 80 per cent of NHS trusts reported problems with ants, 66 per cent with rats and 77 per cent with mice.

Cockroaches were reported at 59 per cent of trusts, biting insects or fleas at 65 per cent, and bed bugs at 24 per cent.

There were infestations of maggots at a further 6 per cent of trusts. And many of the pests were in clinical areas.

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The data, revealed under the Freedom of Information Act, shows that, on average, every trust in the country calls out pest controllers once a fortnight.

At one hospital, a horrified patient awoke to find maggots in her slippers. At another, expectant mothers were dismayed to find the ward overrun with rats, while at a third hospital, a store for sterile materials was infested with mice.

More than two-thirds of trusts had to call out pest controllers 50 or more times between January 2006 and March 2008.

At one trust alone - Nottingham University Hospital - there were no fewer than 1,070 pest incidents between 2006 and 2008.

Last year's report into the deaths of 270 patients from C.diff at a Kent hospital trust found poor hygiene was directly responsible for the outbreak.

Conservative health spokesman Andrew Lansley said: 'Labour have said over and over again that they will improve cleanliness in our hospitals but these figures clearly show that they are failing.

'It is difficult for Health Service estates to maintain a completely pest-free environment but the level and variety of these infestations is concerning.

'We need greater transparency in NHS infection control, and publishing data like this is one way in which we can drive up overall hygiene standards.'

The data reveals that Ipswich hospital had repeated infestations of ants in the dental unit, eye clinic, radiotherapy unit, chest clinic, rheumatology and physiotherapy.

There were biting insects and cockroaches in the X-ray unit, while cockroaches were found in the eye clinic and an antenatal unit. Flies infested the maternity wards.

Mid-Cheshire trust, which runs hospitals in Crewe and Northwich, reported that wards had been ' overrun' with ants, and mice were 'all over' several wards.

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Wards also experienced infestations of rats, bed bugs and biting insects. One ward had a wasps' nest. There were fleas in the orthopaedic department.

Salisbury hospital reported rodent droppings in the sexual health clinic - and a wasps' nest.

Trafford hospital said one ward had 14 separate infestations of ants, while there were also problems with fleas and crickets on other wards.

Mid-Essex trust, which runs hospitals around Chelmsford, reported rats in a maternity unit and wasps in operating theatres.

Dudley hospitals reported repeated infestations of ants in the eye clinic.

Michael Summers, of the Patients Association, said: 'It is outrageous that this should happen in our hospitals in the 21st century.

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'It's a great worry to patients, and does nothing to speed recovery.

'If you're lying in hospital with an open wound, the last thing you want to worry about is rats and cockroaches in the vicinity.'

Despite millions being ploughed into the NHS since New Labour came to power in 1997, many hospital buildings are still dilapidated.

The information collated by the Conservatives amounts to a roll call of failure to improve hygiene in England's hospitals. And the number of infestations is likely to be greater because only three-quarters of trusts responded to the Freedom of Information requests.

Clive Boase, of Pest Management Consultancy, said insects such as flies, ants or cockroaches can be carriers of superbugs.

He added: 'These infective insects disperse through the hospital, possibly into clinically sensitive areas.

'If they come into contact with a vulnerable patient, there is a chance the patient may then develop a healthcare-acquired infection.'

Christine Braithwaite, of watchdog the Healthcare Commission, said: 'Cleanliness and hygiene are of critical importance to patients and the public. We are inspecting every hospital trust this year.'

She added: 'If we were concerned that the safety of patients was at risk, through poor hygiene standards or in any other way, we would take immediate action.'

Last night health minister Ivan Lewis said: 'There is more than a whiff of hypocrisy in these comments from Andrew Lansley.

'It is the Conservatives who oppose Labour's hospital deep-cleaning programme.

'They also oppose our demanding targets on healthcare-acquired infections which have proved so effective in tackling MRSA and C.diff.'