A man was arrested after a taxi driver who was given fake cash drove the suspect straight to a police station.
Nottinghamshire Police said the driver picked up the suspect from Nottingham Road at 23:30 BST on Tuesday.
When the customer continued to change his route, the taxi driver asked how he would be paying, which is when he was handed a counterfeit £20 note, the force added.
After questioning the customer and being given further fake notes, the driver took him straight to Radford Road police station.
The force said officers also carried out a search of a man’s address, where they discovered a “Rambo knife” under his mattress.
It added no further counterfeit cash was recovered, but a cannabis cultivation kit was seized from the address.
A 23-year-old man was arrested on suspicion of using counterfeit currency and possessing an offensive weapon in a private place.