The Met Office has extended an extreme heat warning for Sunday and Monday, with temperatures forecast to build to over 35C (95F) in south-east England, as an under-pressure hospital declared a major incident. The amber warning comes as extremely high temperatures in Spain and France are expected to push north into the UK this week. Temperatures reached 43C in central Spain on Monday and are forecast to rise further. On Tuesday, Portsmouth hospitals university NHS trust declared a critical incident, citing pressures including “the added strain of the prolonged high temperatures”. The heat and resurgent Covid cases have led to all 10 NHS regional ambulance services in England moving to their highest state of alert. The South East Coast ambulance service said the hot weather was a major reason for the “sustained pressure on both our service and wider [NHS] system”, while the London ambulance service also cited it as a factor underlying the “sustained demand on both our 999 and 111 services”. One senior ambulance service leader in the north of England told the Health Service Journal that patients were having to contend with very hot temperatures as they waited in the back of ambulances outside hospitals to be handed over to A&E staff. Ambulance trusts are bracing for even more intense demand in the coming days as temperatures rise higher. The heatwave could disrupt schools if temperatures become too high in classrooms. The National Education Union said in a safety briefing that “closing classrooms which are unacceptably hot and teaching classes elsewhere, or even sending pupils home” could be considered. The heatwave could also bring further transport disruption. Network Rail said it had introduced temporary speed restrictions at the hottest times on parts of the network, including in Essex, to keep trains running and mitigate the effects of rails expanding in the heat, which can cause buckling. Local authorities, including Hampshire and Lincolnshire county councils, are planning to dust sand over melting roads to soak up excess bitumen. Met Office forecasters said some models predicted maximum temperatures in excess of 40C in parts of the UK over the weekend and beyond, but these were “low probability”. Temperatures in the mid or high 30s are “looking more likely”, they said. The warmest temperature on record in the UK was 38.7C at Cambridge Botanic Garden in July 2019. Downing Street said on Tuesday that planning had been taking place within the NHS, with local councils and across transport networks. “We continue to monitor the results of the heatwave,” the prime minister’s spokesperson said. “There is significant work going on across government in making sure those who are most vulnerable to high temperatures are looked after.” Households in Swindon reported smoke that had spread from a large blaze on Salisbury Plain, possibly sparked by military exercises. Dorset and Wiltshire fire and rescue advised residents to close their windows. Several fires, which started on Monday, were being tackled by the army as they were on military training land where there is risk of unexploded ordnance. An MoD spokesperson said civilian firefighters stood ready to assist should the fire spread. Fire brigades are calling on the public to reduce the risk of fires in parched undergrowth by not throwing cigarette butts or discarding glass bottles that can magnify the sun’s rays. The UK Health Security Agency has issued level 3 heat health alerts for the east and south-east of England, with the rest of the nation having a level 2 alert in place. Dr Agostinho Sousa, the head of extreme events and health protection at UKHSA, said: “If you have vulnerable family, friends and neighbours, make sure they are aware of how they can keep themselves protected from the warm weather.” Level 3 involves issuing media alerts about keeping cool, supporting organisations to reduce unnecessary travel, reviewing the safety of public events and mobilising community and voluntary support. The next step, level 4, is described as a national emergency requiring a multi-agency response, and is declared “in the event of severe or prolonged heatwave affecting sectors other than health”. Downing Street did not rule that out as a possibility on Tuesday. Age UK, a charity for older people, recommends keeping blinds down and windows closed when it is hotter outside than indoors, using a damp cloth on the neck to keep cool, and drinking plenty of water and eating even if you do not feel hungry. “We know that extreme heat can aggravate lung and heart conditions, so our advice is to take care and if you are breathless, even after you have rested, to seek medical advice,” said Caroline Abrahams, Age UK’s charity director. “The symptoms of heat exhaustion can be similar to Covid-19 and include a high temperature, excessive sweating and pale, clammy skin and headaches. If you experience any of these symptoms go somewhere cool, rehydrate and cool down your skin with water, fans or cold packs.”