A mix-up over the raising of Tower Bridge led to a ship crashing into the piers of the bridge, according to an accident report.
The report by the Marine Accident Investigation Branch concluded that the sea pilot, the captain and the Port of London Authority each thought the raising of Tower Bridge had been booked.
The crew aboard the tall ship tried to avoid the bridge when they realised it had not been raised but was unable to stop in time and ship's port side was damaged in the crash.
The ship is owned and managed by the Jubilee Sailing Trust which runs hands-on sailing holidays for disabled people.
The MAIB recommended a tightening of procedures to ensure such an incident could not happen again.