London Underground recorded a sharp drop in passengers on Tuesday as commuters opted to work from home as temperatures soared to record levels.
Transport for London, which has advised people to “only travel if essential”, said around 1.03 million entries and exits were made by London Underground passengers up to 10am on Tuesday.
The figure was down 30% compared with the same period last Tuesday, and also lower than Monday’s figure of 1.06 million.
Some 1.04 million bus journeys were made up to 10am, a decrease of 16% week on week, and down from Monday’s figure of 1.07 million.
The drop in passengers came as the temperature exceeded 40C in the UK for the first time on record, with 40.2C reported at Heathrow around lunchtime, according to provisional Met Office figures.
Shelves in some supermarkets were stripped of water as people kept hydrated and supplies of ice cream were also running out in other stores.
Members of the Household Cavalry have been using electric fans to help them cope with the rising temperatures in London.
Troops were looking red in the face and sweating while standing watch in their heavy ceremonial uniforms and helmets at Horse Guards Parade in Westminster, as the heatwave continued to hit the UK on Tuesday.
One could be seen stood in position with a large metal desk fan pointed towards him in a bid to keep him cool.
Water was brought out to the horses of the mounted troops.
Brian Jordan, director of 999 operations for London Ambulance Service, said the service saw a slight increase in calls for fainting and heat exposure on Monday.
The service received 6,600 emergency calls yesterday, which was slightly lower than predicted.
"We really hope that’s because the public really have been listened to the messages about how they can look after themselves and only call 999 if it’s a genuine emergency,” Mr Jordan told BBC Radio 4’s Today programme.
"People have been through a very long day yesterday and there’s been high temperatures overnight and with the even hotter temperatures today, I cannot really emphasise enough that people need to continue to do what we were asking them yesterday – to avoid prolonged exposure to the sun, keep hydrated, look after more vulnerable friends, families, neighbours and use sun cream etc."
He added: "As yesterday afternoon progressed we saw a slight increase in the rates of fainting and heat exposure."
Mr Jordan said that the service expected to see a "build-up of illness due to the continued heat overnight and even higher temperatures coming today… it’s just about making sure that even after the peak temperatures, everyone continues to follow that advice".
Ambulances were not waiting outside of hospitals any longer than usual on Monday, he added.
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