At just 4in (10cm) long and 2in wide it could easily pass for a key fob. But it can fire .22 bullets and has become the latest alarming symbol of the British obsession with carrying a weapon.

Marcus Henry, 27, will be sentenced today for using one to shoot a stranger after a row outside the Departure Lounge bar in the City of London. As he tried to drive away, clubbers, including City professionals, rushed his car and smashed all the windows. Yaw Darko Kwakye, 24, had the bullet removed from his shoulder in hospital.

Key-fob guns are made in Bulgaria to fire miniature flares, but British police forces have been told to watch out for a batch of 100 that were converted to fire bullets and smuggled into Britain. They are cocked by pulling part of the keyring and have buttons on the side to fire them and to open them for reloading.

The gun used by Henry was found hidden in a sock with traces of Henry’s blood on it during a police search of a house. Superintendent Colin Cowan, who led the investigation into the shooting, said: “Although officers have heard about these guns, not many have come across one before. I had received warnings about them being used before but never seen one until now.”

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