A discarded cigarette is suspected to have started the fire that caused some €20 million worth of damage at Britain's National Motorcycle Museum.
Although more than 400 of the 800 exhibits at the attraction near Birmingham were saved in yesterday's fire, it is a massive blow to the history of motorcycles.
Hundreds of vintage motorbikes, many of them irreplaceable and having been used in world record feats and events such as the Manx TT, were wiped out.
West Midlands Fire Service said today that a cigarette butt which a member of staff may have thrown away in a designated smoking area outside the building was responsible for igniting a small pile of cardboard boxes, leading to yesterday's massive blaze.
At its height, more than 120 firefighters tackled the blaze, which could be seen from 15 miles away. Crews were still at the scene this morning.
Staff and delegates at a business conference taking place at the museum managed to wheel out around hundreds of motorcycles.
The machines were part of a collection charting the history of the British motorcycle industry. Exhibits from the five display halls included BSA Gold Stars, Sunbeam Twins, DMW Hornets and Triumph racers.