People were stopped from entering or leaving the BBC's Broadcasting House on Monday as police investigated what they said was a suspicious vehicle.
BBC Broadcasting House sealed off over 'suspicious van'
A bomb disposal robot approached the orange van and a number of controlled explosions were carried out.
Roads were closed around the area in central London and BBC staff were advised to stay away from windows.
Police cut open the doors of the van, which was found to contain cardboard boxes and a motor bike.
All entrances and exits of New Broadcasting House were closed at around 16:50 BST while police carried out their investigations on nearby Duchess Street, which is to the rear of the BBC's headquarters.
It left some staff unable to return to work - and others unable to leave. The building reopened at 18:30.
Scotland Yard said all roads were re-opening.
An AI conference was also taking place at the building at the time.
One participant tweeted it had been a "surreal" afternoon.
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