WDC Liz Phillips (Celia Gregory) carries a Smith & Wesson Model 36 in "A Hole in the Bucket" (S03E02). In "A Touch of Eastern Promise" (S03E06), Adnan Rashid (Zia Mohyeddin) holds a Smith & Wesson Model 36 that is then taken from him by Zaki Mansoor (Nadim Sawalha). Julian West (Edwin Richfield) uses a Smith & Wesson Model 36 in the climactic scene of "Tug of War" (S03E09).
Unidentified Revolver
Security guards at Gervase Ewell's estate carry holstered revolvers in "House Guests" (S03E10). These full size handguns with wide grips may be some Smith & Wesson or Colt models.
Pistols
Walther PPK
Skinner (Bruce Lidington) holds a Walther PPK in the climactic scene of "A Hole in the Bucket" (S03E02).
Walther P38
An unnamed hitman (Giles Meredith) uses a suppressed Walther P38 during the assassination attempt in "A Hole in the Bucket" (S03E02).
Luger P08
Brigadier Wimble (Ralph Michael) fires a Luger P08 at fleeing burglars in "The Company You Keep" (S03E08).
Walther P5
Mercer (Jonathan Kent), the leader of a leftist terrorist group, is armed with a Walther P5 in "House Guests" (S03E10).
An antique pistol is seen on the wall in George Thomas's estate in "Ice Maiden" (S03E04). The furnishings of the house are also used in "S.P.A.R.T.A." (S05E06), and the pistol is probably the same flintlock gun.
Submachine Guns
Uzi
Hoesler (Patrick Field) is armed with an Uzi in "House Guests" (S03E10).
Shotguns
Unidentified Shotguns
A pair of long guns are briefly seen in George Thomas's estate in "Ice Maiden" (S03E04). The furnishings of the house are also used in "S.P.A.R.T.A." (S05E06) where what are likely the same guns are seen better. Judging by the view in Season 5, they can be identified as shotguns, either single barreled or double barreled.
Rifles
Unidentified Rifle
In the climactic scene of "House Guests" (S03E10), a police officer of a special unit holds a rifle, possibly a sniper rifle, that is seen very briefly and in the distance.
Trivia
In one scene in "The Company You Keep" (S03E08) a historical site with a German coastal gun of unclear model is seen. The walled concrete platform matches the position of the real Battery Lothringen on Jersey, but the gun itself is different from the 15 cm SK L/45 naval guns that were used on that battery.