Special forces were divided into teams for a hostage scenario at GCHQ. They were supposed to fire paintball-type bullets but one was hit in the arm with a live round

They are the elite British soldiers who can be relied upon to keep a cool head under the most extreme pressure in the harshest environments.

Sometimes, however, even the best of the best have mishaps, as two SAS operatives discovered the hard way when one of them accidentally shot the other in the arm with a live bullet during an exercise at GCHQ.

It happened during a mock operation at the intelligence agency’s headquarters in Cheltenham, known as the Doughnut for its shape.

Two SAS teams took part, one playing an attacking force that invaded the base and took spies hostage, and the other working against them to rescue the kidnapped staff and regain control of the building. The soldiers were supposed to be firing