A Cavalry Guard fainted on the Mall during a procession rehearsal today as a health alert was issued following tropical temperatures.
Pictures show the solider lying face down on the floor as he holds onto his rifle.
Another guard can be seen helping the soldier back to his feet.
Temperatures rocketed to 25C across London at midday, according to the Met Office, before reaching 27C later in the afternoon.
Pictures show the soldier lying face down on the floor as he holds onto his rifle
Getty
A yellow heat health alert has been issued by the UK Health Security Agency (UKHSA) and Met Office for most of England.
It comes as forecasters suggest temperatures could peak at 32C in parts of the UK by Thursday.
A procession rehearsal was carried out today ahead of a state visit by the Emperor and Empress of Japan later this week.
Weather experts warn of a likely "increase in mortality across the population" from today until Thursday.
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Liam Eslick, a meteorologist at the Met Office, said: "According to the latest models, there is a chance temperatures could reach 30C.
"It’s not guaranteed but this will likely be towards the South-East of England, particularly London, Essex and Kent."
The health alert from the UKHSA and Met Office came into force at 8am and remains in place until Thursday afternoon.
The warning has been issued for every region except the North-East.
Another guard can be seen helping the soldier back to his feet
Getty
Eslick added: "My advice to people would be by all means go out and enjoy. They have been waiting for summer.
“But UV levels are going to be high and the sun will be very intense. Wear protection like sun cream, stay hydrated and try to get some shade in the midday sun.
"People sensitive to the sun should take particular precautions."