A man wielding a handgun and drill sparked an armed stand-off in Hemel Hempstead’s Warners End on Sunday evening.
More than 25 officers swooped on the shopping precinct in Stoneycroft after reports of an armed man, who threatened staff and shoppers in the Co-op and Corals bookmakers, just before 4pm.
He struck an elderly shopper in the face with his gun before fleeing into a nearby block of flats.
Firearms officers surrounded the block, closing off surrounding roads, before storming in, tasering a 44-year-old and arresting him at around 6pm.
A man from Hemel Hempstead, who was arrested on suspicion of possession of a firearm with intent to commit an offence, remains in police custody.
Paramedics took the assaulted shopper to hospital. His injuries are not believed to be serious.