More than 12,000 people are needlessly dying or becoming disabled each year following a stroke, according to a charity.
Some 100,000 people a year suffer a first stroke
The Stroke Association said a lack of specialist stroke units in NHS hospitals was to blame.
It described the situation as "a national scandal" and urged ministers to take action.
But ministers say the figures are out of date and improvements are being made to stroke services.
According to the Stroke Association, somebody in Britain has a first stroke every five minutes. That amounts to 100,000 people a year.
About 10,000 are under the age of 55 and 1,000 are under the age of 30.
Stroke is one of the country's biggest killers and is the single biggest cause of adult disability.
In 2001, the government published its national service framework for older people.
It pledged that every hospital in England and Wales would have a specialist stroke service by April 2004.
According to the Department of Health, 83% of hospitals are on target to meet the deadline.
However, the framework failed to define exactly what constituted a specialist stroke service.
According to the Stroke Association, this has led some hospitals to claim they have a specialist stroke unit when they do not.
For instance, some had reclassified wards as specialist stroke units even though they did not have specialist equipment or staff.
Figures from the Royal College of Physicians of London show huge variations in NHS stroke services.
A recent report suggested that in some parts of the country as many as 85% of stroke patients never see the inside of specialist stroke units.
Studies have shown that patients who are treated in specialist stroke units are more likely to survive and are less likely to suffer disability.
"People are dying because stroke is not always treated as the emergency it is," said Jerry Doyle, of the Stroke Association.
"Stroke patients are left on general wards, where there is no specialist equipment or staff. There are delays on brain scans and sometimes no brain scans at all.
"They deserve better treatment than this. It's a national scandal," he said.
"We ask the government to tackle the stroke postcode lottery."
Public Health Minister Melanie Johnson said the figures were out of date.
"We take services for stroke patients very seriously and are working hard to improve the care patients receive in hospital.
"By April next year, 171 out of 181 hospitals will be providing specialist stroke services with a team of dedicated health professionals in place with expertise in this area.
"That's 94% of hospitals that are well on their way to introducing this service. The 83% quoted by the Stroke Association is from 2002 and we've made real progress since then.
"However, I agree with the Stroke Association that services do need to improve and we will continue to build on the progress that has already been made."
Liberal Democrat health spokesman Paul Burstow said:
"Labelling wards as stroke emergency centres without having the trained staff or resources is a cruel deceit which costs lives.
"The tick box and target culture is undermining the public's trust of the NHS. Ministers must stop over-claiming and start delivering."