Britain Braces for Hottest Day of the Year as Exceptional Heatwave Hits A week-long heatwave is expected to bring record-breaking temperatures to the UK, with temperatures set to hit 34C in London on Monday. The Met Office has declared an 'exceptional spell of warmth for May with a notable heatwave forecast', with high pressure bringing settled conditions and clear skies. A UK Health Security Agency six-day heat health alert has been activated for southern, eastern and central areas of England, warning of an 'increased use of healthcare services by vulnerable people' and a 'greater risk to life of vulnerable people'. Britain is bracing for its hottest day of the year so far as an exceptional week-long heatwave begins with temperatures set to hit a record-breaking 34C. The UK is expected to have its warmest-ever May day and spring day over the bank holiday weekend as families embark on their half-term holidays. Temperatures will hit 28C in London this afternoon, beating the current 2026 high of 26.6C recorded in London's Kew Gardens more than six weeks ago on April 8. The mercury will rise further to 29C tomorrow, 31C on Sunday and then peak at 34C on Monday.Tuesday will be 32C then Wednesday and Thursday will both be 29C. Any temperature above 29.4C will be the warmest May day recorded in the UK since 2012 – while the current May temperature record is 32.8C in London in 1922. High pressure will bring settled conditions and clear skies, as the Met Office declared an 'exceptional spell of warmth for May with a notable heatwave forecast'.A UK Health Security Agency six-day heat health alert for southern, eastern and central areas of England was activated at 9am today and will last until Wednesday. This alert – the first since last August - warns of an 'increased use of healthcare services by vulnerable people' and a 'greater risk to life of vulnerable people'. Temperatures in London will hit at least 28C for a week from today, according to the Met Office.Heatwave thresholds - defined as three days in a row at or above a set temperature, which is 28C in London - are likely to be reached in the South East from Sunday. As the weekend progresses, these very hot conditions will become more widespread - extending across central and western England and into parts of Wales.Met Office deputy chief forecaster Steve Kocher said: Temperatures will climb through the weekend, especially in the South, where 30C is likely to be recorded on Saturday and 32C on Sunday. Temperatures are forecast to peak on Monday when we could see 33C recorded in southern England and the Midlands.It is likely that the May and spring UK temperature records will be broken over the Bank Holiday weekend, with forecast temperatures surpassing the existing record of 32.8C. As well as it being hot, there will be lots of dry and sunny weather for much of the UK. There will however be more cloud and some showers in Northern Ireland and western Scotland through the weekend.With relatively low sea surface temperatures there is also likely to be some low cloud and sea fog clinging closely to western coasts. Temperatures in the UK are expected to exceed those forecast in Mediterranean hotspots including Mykonos, Rhodes and Santorini over the weekend. Winds are turning more southerly by the end of the week, but the high temperatures are not primarily due to hot air being transported directly from southern Europe or North Africa.A Met Office spokesperson said: Instead, the main driver of the warming trend is the development of high pressure over and near the UK. As this high-pressure strengthens, it causes sinking air in the atmosphere. This descending air is compressed as it moves downward, leading to warming through a process known as adiabatic compression. In simple terms, as air is compressed, its temperature increases.This process can significantly raise temperatures at the surface, even when the original air mass is not especially warm. In this case, much of the air over the UK still originates from the Atlantic, but it becomes warmer as it descends under high pressure. This mechanism is a common feature of warmer spells in the UK and is often more important than the transport of heat from lower latitudes.Meanwhile people are being urged to check water quality in bathing spots and sea conditions along coasts before swimming as the UK braces for the scorching weather. The Met Office is encouraging the public to be 'weather ready' by making informed choices on swimming and locations as they head outdoors or to the coast to enjoy the sunshine. Campaign group River Action warned of the health risks posed by poor water quality, even in designated bathing spots.Alzheimer's Society said people with dementia are likely to be more vulnerable in warmer conditions and outlined measures others can take to support them. Similarly, the British Heart Foundation said heart patients also face potential dangers in the heat and should take extra precautions to minimise health risks. Hotter conditions often lead to a surge in ambulance call-outs and Royal National Lifeboat Institution (RNLI) rescues along UK coastlines as people experience heat stress or get into trouble in the water