A discarded cigarette caused a blaze leading to 6 million pounds of damage to a stately home.
An official report has accused a plumber for dropping the cigarette during a fag break, which gutted Grade II listed Moreton Hall last March.
The plumber was in the team doing maintenance checks in the roof of the Edwardian mansion, which is now part of an agricultural college.
"The lad is very upset. He has admitted dropping the cigarette, but there is no proof that it started the fire," the Mirror quoted Paul Lockyer, managing director of the Magna Heating Company, based in Warwick, as saying.
"There were other people, including students, around at the time. The truth is we will never know for sure what caused the fire," he added.
Ian Tonner of Warwickshire Fire Service confirmed that it was an accident.
"A worker had gone on to the roof for a cigarette. He dropped it down a hole he thought was a drain pipe - it was a hole in the roof," he said.
The fire destroyed the roof and the lavish interior, including oak panelled walls.
Restoration work is due to be completed next year.