Police seized a stun gun in Chatteris on Friday night after a tip-off from a member of the public.
The gun - designed to temporarily incapacitate a person but usually without causing long term harm - was disguised as a torch.
The weapon is prohibited under Section 5 of the Firearms Act; police confirmed their investigation was ongoing.
Police said the Fenland neighbouring policing team were involved and the seizure was part of their Operation Raptor campaign to tackle crime.
A police spokesman said: "Operation Raptor is about working together across units as one team to make the most efficient use of resources and be as effective as we can.
"Using and highlighting every opportunity we have to tackle and prevent crime, while building trust and confidence in our communities.
"Operation Raptor covers activity such as days of action, targeted patrols and warrants - anything that demonstrates us utilising opportunities to proactively police the county."
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