All patients with suspected stroke should be able to get immediate CT scans 24 hours a day, seven day a week, according to new guidelines.
The National Institute for Health and Clinical Excellence (NICE) and the Royal College of Physicians said people suspected of having a stroke should be admitted to a specialist unit where they should receive clot-busting drugs as soon as possible.
Those who have suffered a transient ischaemic attack (TIA) - sometimes called a "mini-stroke" - should also be diagnosed and treated within 24 hours.
A TIA causes stroke-like symptoms which usually disappear within a day, but it could signal that somebody is about to have a full stroke.
A total of 20,000 people have a TIA in England every year and more than 110,000 have a stroke.
About 50,000 people die from stroke each year and it kills more women than breast cancer.
The guidelines, aimed at pushing up the quality of care for stroke patients, said stroke units should have immediate access to medical staff specifically trained to deliver thrombolysis (clot-busting drugs) and treat stroke patients.
They also recommend that all patients with suspected stroke should be tested with the Face Arm Speech Test (Fast) or a similar test to recognise symptoms of acute stroke.