The Metropolitan Police reported receiving “numerous 999 calls within a short space of time” that triggered its own anti-terrorism emergency response. British Transport Police said it had received a report of shots being fired on the platform at Oxford Circus Underground station.

Armed officers flooded the area. Oxford Street and the busy Tube stations at Oxford Circus and Bond Street were pressed into lockdown. Shoppers were urged to take cover in nearby buildings. The department stores that dominate the street, among them John Lewis and Selfridges, shut their doors and gave shelter.

Twitter users went into overdrive. On Facebook, people posted photographs of loved ones whom they could not contact and feared were missing. Olly Murs, the pop singer with almost eight million Twitter followers, posted at 5pm: “Everyone get out of Selfridges now gun shots!! I’m inside”, followed eight minutes later by “Evacuating store now!!! F--- heart is pounding.”

He would later, somewhat unfairly, be ridiculed for issuing such an overdramatic account but he was not alone in expressing his heartfelt terror.

Greg Owen, a 37-year-old Londoner, was certain the capital was under attack. “Guy with gun on Oxford Street near Oxford Circus I’m in the middle of it. Currently taking cover in French Connection,” he tweeted.

A quarter of an hour later he remained gripped by fear. “Latest update from the police ‘we can’t give you specifics. But there’s been shots fired and explosives. So please stay in the shop and move to the back’.”

Armed officers and ambulances raced to the scene. “Police have responded as if the incident is terrorist related,” said Scotland Yard in a statement issued at 5.16pm, 38 minutes after the first calls came in. “If you are on Oxford Street go into a building and stay inside until further direction,” came the advice, adding: “Avoid travelling to the Oxford Street area.”

Sophie Foster, 22, was having a drink with friends in a nearby bar. London had suffered four terrorist attacks this year already and Black Friday seemed an obvious and ominous day to target, highlighting tensions in the run-up to Christmas.