A shopper used more than 20 counterfeit notes to pay for goods at Sainsbury’s in Woodhall Farm.
Now police have released a CCTV image of a man they want to speak to in connection with the incident, which happened between 2.30pm and 2.50pm on Saturday.
PC Lazarus Clark said: “He may have been a witness to the incident or may have some information which could help the investigation. If anyone recognises the man pictured, or if you recognise yourself, please get in contact as soon as possible.
“I urge residents and business owners to be aware of people attempting to use and pass on fake currency in the Hemel Hempstead area. During November there were other reported incidents of individuals approaching shoppers in the town centre attempting to get change from counterfeit £20 notes.
“If anyone believes they may have been approached by someone trying to defraud them of money or believes they are in possession of fake currency they should contact me.”
Contact PC Lazarus via the non-emergency number 101, quoting reference D1/13/ 6692.