By Nick Triggle
Health reporter, BBC News
A&E units have to see patients within four hours
Hospitals are fiddling a four-hour A&E wait target by using other wards as dumping grounds, the Conservatives say.
Data from 114 NHS trusts in England found many patients faced long waits in assessment units which did not count towards the waiting time.
Over a fifth of units reported keeping patients longer than the recommended 24 hours with the average wait being 17.
Doctors agreed the system was being abused in places, but the government said the research was "misleading".
The Conservatives asked hospitals to provide data on their use of these wards under the Freedom of Information Act.
The units are commonly known as emergency assessment or clinical decision units.
They effectively act as a half-way house between A&E and hospital to allow patients to continue to be monitored before a decision is taken to continue treating them or discharge them.
Many are mixed-sex and do not have proper beds, leaving patients to rest on trolleys.
Shadow health secretary Andrew Lansley said: "Labour complacently claim that they have abolished long waits for patients being admitted to hospitals, but these figures show that all they have really done is fiddle the figures.
"It is unacceptable and has to change."
It is not the first time the way the target is being met has been criticised.
Both the British Medical Association and academics at London's City University have raised concerns over the last few years about the use of assessment units.
John Heyworth, from the College of Emergency Medicine, said the four-hour target, introduced in 2004, was not working as well as people believed it was.
"There is a continuing amount of gaming going on," he said.
"We know these areas are being used frequently purely to admit patients to meet the target and quite often they are not properly equipped or staffed."
He said doctors would like to see more flexibility in the target to allow them to continue monitoring patients for longer than four hours when appropriate.
Nigel Edwards, policy director of the NHS Confederation, which represents hospital trusts, said it was likely patients were being moved to provide more time for tests, as the four-hour target did not give medical staff "very much leeway".
Health minister Gillian Merron pointed out before Labour came to power patients were facing long waits.
She said the Tory figures were "misleading" as some of the units were observational wards which had been designed and equipped to care for patients for a while.
But she added: "We expect assessment units to be used to improve patient care, not as a 'holding area' or to avoid breaching the A&E four-hour standard."