The man met his match when he demanded money from Edinburgh newsagent Mohammed Afzah, a former police bodyguard for the prime minister of Pakistan.
The robber was forced to flee empty-handed when Mohammed adopted his defensive stance and told him: "Come on and give it a go then."
Mohammed, who was born in Pakistan, spent eight years in the country's security police, where he was trained in hand-to-hand combat and anti-terrorist techniques, before guarding politicians and VIPs as a bodyguard in Lahore.
He told Convenience Store: "The robber ran in to my store waving a knife and screaming at me. He told me over and over again to hand over money from the till, but I wasn't going to give him anything. Instead, I started shouting back at him and looked into his eyes and told him to come and have a go. I definitely scared him and he ran away. I would do the same again, but I wouldn't recommend other retailers do the same. I acted like I did because I knew what I was doing."
Mohammed has handed over CCTV footage from the raid, which police are studying in an attempt to identify the would-be-robber.
l For more on retailers who choose to fight back, and advice on best practice, see Zero Tolerance p30.