A forensic examination of the remains of the Cutty Sark damaged by fire has failed to establish how it started.
The 138-year-old vessel is a renowned visitor attraction
Scotland Yard said tests on the remains had proved "inconclusive" as to how the fire began.
Firefighters were called to the scene in Greenwich, south-east London, in the early hours of Monday to find the 138-year-old tea clipper ablaze.
The vessel was undergoing a £25m restoration and much of the ship had been removed as part of the repairs.