The bomb was in the Haymarket, near the popular Regent Street shopping area, and security sources say it could have been timed to coincide with Gordon Brown's first day as Prime Minister.
An eyewitness said a man had crashed the vehicle into bins near Tiger Tiger and then ran off, before the alarm was raised.
The timing coincided with hundreds of revellers leaving nightspots, but police said there was no intelligence to suggest such an attack.
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