UK weather - live updates: Hottest day of the year recorded as heatwave sees Heathrow hit 35C

We have a new record!

The Met Office is now reporting temperatures of 34.4C at Heathrow in west London.

The Independent's Science Correspondent Josh Gabbatis is here to explain the heatwave in full for your viewing pleasure:

Yeesh. We're now up to 35C at Heathrow and forecasters are suggesting we could see 37C on Friday, potentially triggering a mid-afternoon thunderstorm.

Stay cool out there.

A brief update of how the weather is taking its toll across the country: 

- The heatwave is said to be causing "winter conditions" in parts of the NHS

- Passengers on Eurotunnel endured five-hour delays with no air conditioning

- The Royal College of Nursing said high temperatures were leaving nurses dizzy and exhausted

- 56 fires have raged on grass verges next to England's motorways

- A high pollution alert was issued for London

- Fire brigades are calling for a ban on BBQs in parks

Here are some of the key temperatures that could be matched or surpassed before the weekend:

33.3C: highest temperature recorded so far this year, on July 23 at Santon Downham in Suffolk

34.5C: highest recorded last year, on June 21 at Heathrow airport

35.6C: highest recorded in 1976, on June 28 in Southampton

36.7C: highest July temperature on record, set on July 1 2015 at Heathrow airport

38.5C: highest temperature ever recorded in the UK, set on August 10 2003 at Faversham in Kent

A warning from the Met Office.

Rush-hour commuters on the London Underground sweltered in temperatures above the legal limit for transporting livestock on Thursday, the hottest day of the year so far.

Temperatures reached 35.7C (96.26F) on the Central Line, while the Bakerloo, Victoria and Jubilee all were several degrees above the 30C (86F) maximum for transporting cattle, sheep and pigs, the Press Association found.

Sweat-soaked passengers fanned themselves and gulped down water as the humidity in some carriages rose above 60%.

However commuters on the air-conditioned Circle Line enjoyed more tolerable temperatures of 29.4C (84.92F).

It comes after commuters battling "unacceptable" conditions were told they must wait more than a decade before air-conditioned trains arrive on some of the capital's busiest routes.