A small explosion at London’s Tower Hill station sparked an evacuation causing a slight panic and fears of a terrorist attack, but it was instead a mobile phone that had exploded after being plugged in to charge.

Dai Rees, 56, from Thames Ditton, was on the train when he noticed a bag “sparking like a fire cracker”.

“A lot of sulphurous smoke appeared out of the container which was attached to a thin wire going into the bag,” Rees said.

“At that time everyone started screaming and running in two directions.

“It (the bag) started jumping around and sparking. It all happened within 10 or 20 seconds.”

This latest event adds to the series of incidents of exploding phones majority of which were Samsung Galaxy Note 7’s that had to be recalled.

Laptops, mobile phones and even e-cigs have all been implicated in explosions that are caused by batteries catching on fire.

Manufacturing errors mean if batteries charge too quickly they can generate excess heat, leading to a short circuit.

The possibility of defaults has seen recalls and some electronic bans on flights.