Thermal images show just how hard it is to keep cool in London

A new smartphone camera, that visualises heat that is invisible to the naked eye, has shown London's recent heatwave from a whole new perspective.

The Cat S60 is the world’s first smartphone with an integrated thermal camera which highlights temperature contrasts using blue for cold and yellow and red for hot.

The device was taken for a spin around London during the recent mini-heatwave - and the images revealed intense pockets of heat, particularly around commuters.

Londoners glowed red in 36C heat on the Central line, and a soldier on Whitehall was luminous in his uniform at almost 33C - the camera picked out his face as his hottest part.

Bullitt Group, which makes the phone, said it could be useful for firefighters to see through smoke to find the origin of a fire.