Watches of Switzerland had its Knightsbridge store raided on Black Friday by two armed robbers on a motorbike.
The criminals are believed to have made off with £40,000 worth of stock from the Brompton Road shop.
The only weapon found at the scene was a discarded sledgehammer, which the attackers used to smash down the front door of the luxury boutique.
Witnesses from the surrounding area, including a nearby Swarovski store, said that there were no security workers on hand to deal with the break-in as it unfolded.
Police say that no-one was injured in the raid and no arrests have been made.
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