The four-hour A&E target is being "fiddled" by "dubious management tactics", academics say.
Patients should only wait four hours in A&E
City University's Cass Business School said to meet the target the NHS needed to treat patients twice as quickly.
They said this was not achievable after using mathematical modelling and suggested hospitals were manipulating the figures.
But the government said it was "nonsense" to suggest the target was not being met.
Since 2004, 98% of patients in A&E should be seen within four hours. Latest figures show this is being achieved.
Researchers analysed data from 170,000 patients and used "queuing theory", a recognised model to predict people flow used by supermarkets and traffic monitoring systems.
The academics were then able to show how quickly hospitals could treat and discharge people to meet the target.
They found that patients would need to be seen and cleared from A&E wards within an hour.
Before the target kicked in, patients were seen in just under two hours.
The researchers said this level of improvement was not achievable, although they did not doubt that waiting times had reduced.
Instead, they suggested hospitals were using tactics to stop the clock.
They said there was a peak of patients being discharged at the four-hour mark, and suggested hospitals may be discharging them and then readmitting them straight away.
The academics also said hospitals were moving patients to clinical decision units, a kind of half-way house between A&E and the rest of the hospital.
In these departments, patients still remain under observation before a decision is made on their treatment, but it is not classed as an A&E wait.
Lead researcher Professor Les Mayhew said: "The current A&E target is simply not achievable without the employment of dubious management tactics.
"The government needs to revisit its targets and stop forcing hospitals into a position where they look for ways to creatively report back, rather than actually reducing waiting times for real people."
The report comes after a British Medical Association survey of doctors last month suggested a third thought data was manipulated to achieve targets.
Martin Shalley, president of the British Association of Emergency Medicine, said the four-hour target had put doctors under "huge pressure".
"I don't think doctors are fiddling the figures as such, but we do know that waits in other parts of the hospital, such as clinical decision units, are increasing because the pressure comes off."
A Department of Health spokeswoman said: "It's absolute nonsense to suggest that the A&E waiting time standard is not being met.
"Ask patients and they'll tell you the same - more patients say they now wait less time in A&E and are more satisfied with their treatment."