Temperatures reached a scorching 33C at Heathrow on hottest day of the year so far.
People have been warned to stay hydrated while out and about in the hot conditions, with people flocking to beaches in huge numbers despite social distancing measures still being in place.
Hundreds of people made the most of the hot weather on the beach at Southend.
An amber level three heat-health alert, issued by the Met Office, was extended on Thursday.
The warning requires social and healthcare services to target specific actions at high-risk groups, according to the Met Office website.
Health authorities have encouraged those most vulnerable – many of whom have been shielding during lockdown – to protect themselves during the “exceptionally hot weather forecast this week”.
Public Health England said older people, those with underlying health conditions, and very young children were all more at risk from the higher temperatures.
The Met Office has issued a yellow warning for thunderstorms across Northern Ireland, Wales and the west of Scotland and England, with the storms set to move eastwards into Friday.
The rainfall brings a risk of flooding and disruption to some places.