London and the south east of England are expected to see the highest temperatures, but northern areas will also hit the low 30s.
In South-West London, the high will be around 37 degrees.
The top high for 2020, of 37.8 degrees Celsius, was recorded at Heathrow a week ago.
Forecaster at the Met Office, Craig Snell, says it's rare for it to be this hot two weeks running.