Temperatures expected to hit 40C in parts of the UK, as extreme heatwave spreads slowly eastwards, sparking warnings in Italy and the Netherlands France records hottest day ever as 40 people drown across country Tell us: how is the heatwave in the UK and across Europe affecting you? London mayor Sadiq Khan has triggered a “high” air pollution alert for the capital on advice from forecasters at Imperial College, the third one this year. The heat has forced the army to cancel ceremonial operations in London and Windsor, to protect the “wellbeing” of its soldiers and horses.