A seven-day target for seeing patients after a "mini-stroke" is routinely missed, but may not be helping patients anyway, say experts.
Manchester University researchers found that on average, patients waited 15 days after a "transient ischaemic attack" (TIA) for an appointment.
They say many have full strokes in the week after a TIA and that urgent assessment would be better.
The study appears in the Journal of Neurology, Neurosurgery and Psychiatry.
The Stroke Association has supported the call for immediate treatment.
A TIA involves some of the symptoms of a full stroke, but the effects may be short-lived and mild.
However, in some cases having a TIA means a patient is at a higher risk of having a stroke shortly afterwards, perhaps causing permanent damage.
Currently, guidelines suggest that TIA patients should be seen within a week at a "rapid access" specialist clinic, although only a third of trusts are meeting that target.
The Manchester researchers looked at 711 cases in the north-west of England, and found that on average, the delay was more than two weeks.
Curiously, they found that the rate of strokes among the patients who reached the clinics was lower than expected.
Dr Craig Smith, one of the researchers, said that the most likely explanation was that some patients did not meet appointments because they had already had a second TIA, or even a stroke, in the intervening period and had died or were in hospital.
This means, he said, that the current system might not be set up to catch those at high risk of further problems.
He said: "This was the only real explanation for the discrepancy. We are missing all of these high-risk patients."
He said that even a seven-day target left high-risk patients in danger before seeing a specialist.
He says the evidence now favours treating TIA more seriously, and either assessing patients on the spot for their risk of a subsequent stroke, or even keeping them in hospital.
"It is increasingly going to be proposed that it's difficult to justify not admitting people following a TIA."
Joe Korner, from the Stroke Association, said that quick treatment following a TIA could reduce the risk of major stroke by up to 80%.
He said: "This research further strengthens the need for everyone who experiences a TIA to be treated urgently.
"This vital and urgent treatment of TIAs does not require brand new technology; it is simply about organising services to enable TIAs to be treated with currently available treatments quickly.
"A TIA is a warning sign that a major stroke may be on the horizon, but all too often people either ignore the symptoms or aren't aware of what the symptoms of stroke are.
"We urge anybody who is experiencing facial weakness, arm weakness or speech problems to dial 999.
"It is hoped, following the launch of the National Stroke Strategy towards the end of this year that more will be done to increase public awareness of stroke and its symptoms and that patients with TIAs will be assessed and treated within 24 hours, which is vital." ( BBC )