PSNI issues the Glock 17 to all constables. Visible in several episodes, but especially this one, all the actors appear to be carrying Glock 18 machine pistols. These are easily distinguished by a prominent selector switch on the side of the slide.
Visible in several episodes, the Glock pistols carried by all the PSNI constables, especially when not in the holster, are too shiny (the slides appear to be made of plastic, not steel), have slightly incorrect shapes, visible seams, and are clearly too light when handled. They are obviously props or models (possibly airsoft guns).