Schools are cancelling sports days and allowing pupils to wear PE kits in lessons this week as Britain enters its third heatwave of the year with 34C highs on the way.Headteachers are urging parents to send their children in with sunscreen, hats, water bottles and handheld fans amid concerns over temperatures rising once again.The Met Office expects highs of between 31C and 34C each day between today and Sunday in London – with the hottest weather anticipated today and Thursday.Some schools have called off sports days because of fears for pupils' safety in the hot weather, and are unable to reschedule the events before the summer holidays.The Department for Education issued fresh hot weather guidance last Friday, saying that schools are 'generally expected to remain fully open, with sensible adjustments made to reflect local conditions and the unique features of each school'.Parents were told the changes might include relaxing uniform requirements, moving lessons into cooler parts of the school and increasing access to drinking water.Teachers may also use shaded outdoor spaces for learning, adjust classroom layouts to improve airflow and ventilation and look at 'rescheduling physical activity'.Schools should only close 'because conditions are unsafe', but parents were told they can then 'expect some form of remote education where reasonably possible'. Cyclists sit in the warm sunshine on a parched Wimbledon Common in London yesterday The UK Health Security Agency heat health alert for parts of England will run until Saturday