Alston Hall near Longridge was ripped apart by a blaze on Wednesday, March 15 and fire service investigators have now ruled out arson.
An extensive two month enquiry into the cause of the huge fire came to head yesterday with a definite conclusion expected next week.
A spokesman for Lancashire Fire Service said: “It’s looking like the cause of the fire was accidental but that should be confirmed in the next seven days.
“We’re not in position to say how it started but we have pretty much ruled out it being started deliberately.”
More than 70 firefighters tackled the blaze, which broke out at the three-storey mansion. Crews in 10 fire engines fought the fire using water from a nearby pond.
The gothic-style mansion was in the middle of being renovated by its private owners when it caught fire.