This Glock 17 pistol, with thumb safety, was designed by Glock for use by the British Army. It was on display at DSEi ’09.
This is not the first Glock designed with a manual safety. Glock has previously designed a Glock 17 for the Tasmanian Police force that featured a standard 1911-style thumb safety.
This safety works differently. In order to engage the safety, it is pushed through the frame with the thumb, much like the magazine release. Disengaging the safety is done with the trigger finger.
At first I thought what a ridiculous mechanism this was until it was explained to me that the SA-80, the British Army service rifle, has a very similar safety which is manipulated in the same way. Glock designed this safety so that it would be familiar to British troops. Very clever!
One problem I do see is an operator going for the magazine release and accidentally engaging the safety. At best it would make the magazine change take longer, at worst the operator could forget to disengage the safety and pull the trigger at a bad guy only to find nothing happens.
I do not know if the British Army are considering replacing their current service pistols or if Glock is just making sure they have a model ready if they do in the future.
Big thank you to Lusaka for the information and photos.