Failings in stroke care are leaving thousands dead or unnecessarily disabled each year, warn experts.
The Stroke Association says too few patients are treated in specialist stroke units, or given the right drugs.
The National Institute for Clinical Excellence and Royal College of Physicians hope new guidelines for England and Wales will help boost care.
The Department of Health said its stroke strategy for England was already improving care.
Each year, approximately 150,000 people in the UK suffer a stroke, and 67,000 people die as a result.
However, specialists say that the toll of deaths and permanent disability could be radically reduced if the NHS offered the appropriate care at the appropriate time.
The latest figures suggest that fewer than two-thirds of patients are treated in a dedicated stroke unit, and many more than at present could receive "clot busting" drugs shortly after their stroke to reduce the long-term damage.
The Royal College of Physicians (RCP) said that approximately 4,500 patients a year were suffering an avoidable disability because these drugs were not given.
It estimates that the number who die because their care is compromised also runs into the thousands.
Straight to specialists
Together with the National Institute for Clinical Excellence (NICE), it has issued fresh comprehensive guidance about the care of stroke.
For the first time, this says that patients with suspected stroke should go straight to the nearest stroke unit rather than to a non-specialist hospital.
Figures for England in 2006 suggest that only one in five patients is being handled this way.
The guideline also recommends that people who suffer a "transient ischaemic attack" (TIA) - sometimes called a "mini-stroke", are seen urgently by a specialist, as a TIA can be an early warning of a bigger stroke.
Dr Tony Rudd, from the RCP, said that implementing the guidelines would require a "radical restructuring of health services".
He said: "All people involved with treating stroke and the general public who are at risk need to know what is in these guidelines so that fewer people in the UK have their lives devastated by this awful disease."
On the shelf
Joe Korner, from the Stroke Association, said that while there had been improvements in England following the publication of a highly critical National Audit Office report, and the launch of the Department of Health strategy, there was still a long way to go.
"Too often in the past, vital stroke guidelines such as these have been put on a shelf and ignored, causing unnecessary deaths, disability and loss of independence for many thousands of people."
The guidelines cover Wales as well as England, which has not so far benefited from a national stroke strategy.
In Scotland, a similar strategy has been in place for much longer, and the Stroke Association said that services there were generally of a better standard than elsewhere in the UK.
Professor Roger Boyle, the National Clinical Director for Heart Disease and Stroke, said that stroke care was improving.
He said: "The latest figures also show that the number of patients spending any time on a stroke unit has increased from 36% in 2001 to 62% in 2006.
"The challenge now is to make sure that people who have a stroke are spending the majority of their time on a specialist stroke unit."