DCI John Luther (Idris Elba) keeps his father's old Smith & Wesson Model 12 in his apartment. In Episode 1 he is shown to use it every morning to play a deadly game of Russian Roulette before heading to work. In Episode 2, Alice Morgan (Ruth Wilson) discovers the weapon after breaking into Luther's apartment.
Several CO19 officers are seen with holstered Glock 17's as their sidearms. They are never drawn, and remain holstered throughout the series.
Submachine Guns
Heckler & Koch MP5A3
British CO19 officers use the Heckler & Koch MP5A3, fitted with EOTech Holographic sights and tactical lights, in several episodes.
Rifles
Heckler & Koch PSG-1 (mock-up)
Various CO19 snipers are seen armed with the Heckler & Koch PSG-1 during a standoff in Episode 4. The PSG-1 used in this episode appears to be a mock-up built from a full-auto G3 variant; it has the detachable push-pin lower receiver unit of H&K's full-auto weapons, whereas the factory PSG-1 has the none-detachable lower receiver of the HK91 civilian rifles. This weapon also has the lower receiver with "S-F" fire control options, rather than the "0-1" options of the factory PSG-1.
Other
Revolver Water Pistol
Nicholas and Robert Millberry (Steve Robertson) are seen using revolver style water pistol's filled with corrosive acid during their various attacks throughout London in Episode 3 and 4.