The suspects were seized about 400 yards from the world-famous Selfridges department store, a few minutes after cases were smashed on its ground floor at 8.30pm last night.
Passersby reported seeing two axes left discarded at the scene soon after the attack, which occurred half an hour before the Oxford Street store was due to close.
Nobody was hurt in the raid and the police quashed rumours that guns had been fired.
Matthew Carrozo, 28, saw the moped fall on the corner of Charlotte Street and Goodge Street.
He said: ‘It just came round the corner and slipped on a drain cover. The guy in the front was wearing a motorcycle helmet and the person on the back was wearing a burka.
Mr Carrozo, a digital marketing manager, added: ‘As soon as they hit the ground someone ran out of a restaurant and pinned them down - and then other people on the pavement joined him.
Armed police arrived soon afterwards and cuffed the man in the motorcycle helmet before taking him away in a police van.
Paramedics treated the man in the burka for possible neck injuries before taking him away, accompanied by police.
Scotland Yard last night confirmed that two men were arrested after falling from a motorcycle.