Northumberland Police is distributing counterfeit note detection pens to local retailers to help combat the rise in forged notes in the area.

In the past month there has been four incidents of counterfeit £20 notes being passed to retailers in the Hexham, Blyth and Berwick areas of Northumbria. In all four cases, it was only after the incident that the retailers realised that the notes were not genuine.

Northumberland crime prevention adviser Del Graham advised businesses to be on the lookout for forgeries. “We would urge all businesses to be extra careful when receiving notes from customers,” he said. “Any cashier or shopkeeper who has any suspicions should not accept the note and contact the police.”

The number of forged notes in the UK rose from 290,000 in 2007 to 686,000 in 2008. These notes had a face value of almost £14m. The Bank of England has a list of tips on its website to help retailers identify if notes are genuine or not.