Today is the hottest May day on record, with temperatures beating yesterday's record by soaring to a sweltering 35C. The Met Office confirmed the milestone after Heathrow and Kew Gardens provisionally reached 35.0C on Tuesday afternoon.'Until yesterday the highest temperature in May was 32.8C, but we've now exceeded that record on consecutive days by a full two degrees Celsius,' the forecaster said.The temperature is roughly double the average for this time of year - following the hottest May day and night readings ever recorded in Britain: 34.8C and 21.3C.And this morning the Met Office issued a yellow weather warning for thunderstorms across the Midlands between 3pm and 10pm today, advising those from Wakefield down to Bath to watch out for 'low likelihood, medium impact' conditions.The forecaster said: 'Whilst many areas will miss them and remain hot and sunny, isolated thunderstorms are possible this afternoon and into the evening. 'These could bring frequent lightning, large hail, gusty winds and the potential for 30mm of rain in less than an hour.'Experts at the UK Health Security Agency (HSA) have also extended an amber health alert for much of the country into Thursday evening, warning that there could be deaths among the elderly and vulnerable.The heat may 'affect the ability of the workforce to deliver services', it said, and warned that increased demand for power driven by the use of air-conditioning could see parts of the grid overloaded.Train companies have come under fire for blaming 'severe weather' for cancelling services with announcements saying it is 'too hot to go on'. A pair of rollercoasters at Thorpe Park reportedly stopped working on Monday, leaving passengers stranded on the newest ride, Hyperia, and fan favourite Colossus. It is unknown if the heat was to blame.And as millions packed onto sweltering Tubes, buses and trains this morning following the record-breaking Bank Holiday weekend, there was misery to come as train operators axed services due to the 'severe weather'.A number of services were cancelled due to the heat while yesterday passengers were forced off a train in Oxfordshire due to a faulty air conditioning system. Staff handed out water bottles as the train from London Marylebone to Stourbridge Junction, West Midlands, was emptied at Banbury. A video from one of the stricken carriages shows passengers asking 'what's going on?' as they were told they would need to leave before their destinations.