Police have shared footage of a shopkeeper using a mop to fight off a knife-wielding robber suspected of targeting a string of shops in Derbyshire.

The CCTV video was released following seven robberies in Derby and Ilkeston in the past five weeks.

The force said the suspect did not physically injure anyone during any of the robberies – which police are treating as linked – but they said significant sums of money were stolen.

Independent charity Crimestoppers is now offering a reward of up to £1,000 for information.