Wednesday was the hottest day of the year so far, the Met Office has said, after 30.3C was recorded at London’s Heathrow Airport.

Met Office meteorologist Kathryn Chalk said that was the highest maximum temperature recorded this year.

Most of England is under yellow heat health alerts, which will remain in force in eight regions until 17:00 on Thursday.

A yellow alert – issued by the UK Health Security Agency (UKHSA) – indicates that weather conditions could pose a risk to those who are particularly vulnerable.

The UKHSA says minor impacts are probable across the health and social care sector.

Ms Chalk added: “Yesterday we got to 30C and that was the first time we reached 30C since September 10 last year.”

BBC Weather’s Matt Taylor said it will be a humid evening but there will be a “marked change” in humidity levels over the next 24 hours and “things will turn much fresher”.

Thousands of ticket holders have begun filtering into the Glastonbury festival site, which is set to benefit from a sunny week with temperatures forecast to hit 27C on Wednesday before cooling down for the rest of the week.

BBC weather said many places – including Glastonbury – can expect largely dry conditions this weekend, albeit with lower temperatures.

Other areas will experience outbreaks of rain and strong winds with gusts of up to 50mph in places.

Further south, there will be less rain and it won’t be as windy – but it will turn cooler.