The Glock is an incredibly safe firearm, and with the safety on the trigger should not be capable of being fired without finger trigger pressure ..... my guess would be (in the absence of any facts!!!!) that the gun was holstered with the finger on the trigger ....
not the first time.
Not the easiest weapon to have an ND with and usually involves pulling the trigger in some way, not always with the finger. Just one example - officer while wearing his over jacket, holsters his Glock trapping the plastic toggle in the trigger guard within the holster, turns & feels his jacket caught on something, gives it a tug & bang 9mm round into leg. However in this case posted above I have no knowledge of the circumstances and would not speculate as to the cause.
<A police officer has accidentally shot himself in the leg at Putney police station while he was "holstering" a firearm.> ... Sky News 10:56pm UK, Friday 24 January 2014
What's the fine for perpetrating an N.D. in the British Army these days?
glock leg at a guess .kept velly quiet by HMG but too many incidents on record ,bring back the browning hi power at least u could hammer nails in and it wouldnt take your leg