Thermal images taken on London Underground reveal temperatures of up to 42°C

Today marks the hottest day in UK history, with temperatures in the south of the country reaching an eye-watering 39°C.

While most of us would love to spend the day out in the sunshine, sadly duty calls, and we have to make the sweaty journey into work.

For London commuters, this means a journey on the London Underground , which sadly is mostly un-airconditioned.

Now, experts have taken thermal images on several of the London Underground tube lines, to show just how hot it is down there.

An inforgraphic reveals how hot the London Underground was yesterday (FLIR)

FLIR used its FLIR T1K camera to take the snaps, which reveal temperatures of up to 42°C.

A spokesperson for FLIR explained: “Equipped with a 1024 x 768 pixel thermal detector, the T1K includes industry-leading thermal sensitivity of < 0.02°C at +30°C, helping to pinpoint even the most minor differences in temperature levels.

“The FLIR T1K can measure object temperatures in the range of -40°C to 2000°C.”

The Bakerloo line reached 42 degrees (FLIR)

The Northern Line reached 37 degrees (FLIR)

In the photos, the brighter colours (red, orange, and yellow) indicate warmer temperatures while the darker colours (purple, blue, black) indicate cooler temperatures.

The images, which were snapped yesterday, revealed that the hottest tube line was the Bakerloo line, which reached 42°C - the same temperature as Abu Dhabi.

The Central line wasn’t far behind on 40°C, followed by the Jubilee and Victoria lines (38°C), Picadilly, Hammersmith & City and Northern lines (37°C) and Circle line (36°C).

The Jubilee Line reached 36 degrees (FLIR)

The Circle line was 36 degrees (FLIR)

Commuters using the Metropolitan lines were slightly luckier, with temperatures reaching 35°C, while those on the DLR were treated to temperatures of 32°C.

Unsurprisingly, many commuters have flocked to Twitter to vent their frustrations.

One user wrote: “The London underground is punishingly hot how is this city not dead yet?”

At 35 degrees, the Metropolitan line was one of the coolest (FLIR)

The Central line reached 40 degrees (FLIR)

Another added: “If anyone wants to know how hot hell is, go on the London Underground Thursday.”

And one joked: “Literally the only things hotter than the London Underground in this weather are: the earths core, hell, the middle of an active volcano and the filling of a MaccyD’s hot apple pie/cheese toastie when you don’t let it cool down for long enough before biting into it.”