By Kate Holton and Muvija M LONDON (Reuters) -Britain was braced for temperatures to hit 40C for the first time this week, with ministers urging the public to stay at home as the heatwave caused train services to be cancelled, one London airport to shut its runway and some schools to close. Much of Europe is baking in a heatwave that has pushed temperatures into the mid-40s Celsius (over 110 Fahrenheit) in some regions, with wildfires raging across tinder-dry countryside in Portugal, Spain and France. Britain’s government triggered a “national emergency” alert as temperatures were forecast to …