Mutt and Jeff were spies who worked for Britain and MI5 and were members of the Double Cross System.

In April 1941 two Norwegians, Helge Moe (Mutt) and Tor Glad (Jeff) fetched up on a remote Aberdeenshire beach, having travelled by seaplane and rubber dinghy. They immediately turned themselves in to the local police as German spies.

MI5 soon 'turned' them, assigning them their codenames, which were the names of a pair of cartoon strip characters (see Mutt and Jeff). 'Mutt and Jeff' is also cockney rhyming slang for 'deaf'.

Mutt and Jeff's mission was supposed to be one of sabotage, as well as having a secondary intelligence role, reporting via wireless military locations, deployments and civilian morale. MI5 used Mutt and Jeff's radio sets to relay false information, leading the Germans to believe that Britain intended to invade Norway (this activity was a component of Operation Fortitude).