The baking Bakerloo Line was the next hottest. Between 4pm and 7pm, most of its stations were in the highest temperature band, although things got cooler the further south you went. Even in the coolest stations the temperature hovered at about 25C.
On the map the green areas show 26 degrees, moving up to 29 degrees in the yellow areas, with the read areas at 32 degrees centigrade.
In previous tests, temperatures in some carriages during the summer have exceeded 35C, which would make the network officially unfit for transporting cattle.
The Underground hotspots can be seen on this map and more information is on The Times.