As Britain braces for the hottest days of the year so far, doctors are urging people to know the danger signs of heat stroke – a medical emergency that can turn fatal within hours.Triggered when the body overheats and can no longer cool itself down, heat stroke can lead to seizures, organ failure, coma and death if not treated quickly.The warning comes as a blistering heatwave grips the UK, with temperatures forecast to climb towards the high 30s in parts of England and Wales this week.The Met Office has issued extreme heat warnings, while health officials have warned that soaring temperatures can pose a risk not only to older and vulnerable people, but also to otherwise healthy adults and children if they become too hot or dehydrated.Last summer, there were an estimated 1,504 heat-associated deaths in England during five heat episodes, according to UK Health Security Agency (UKHSA) figures. Dr Ann Nainan, a GP specialising in urgent care, said: 'Heat stroke is life-threatening and needs life-saving treatment.'We all need to be able to recognise the early symptoms and take corrective action immediately.'So how can you tell the difference between feeling hot and tired – and a potentially deadly emergency? Here, experts reveal the warning signs, what to do if someone is affected, and the simple steps that could help keep you safe during the heatwave. Britons are sweltering beneath a heat dome - and their health could be at risk