John Howes, of the Devon and Somerset Fire and Rescue Service, said the plumber was 'very upset'.

"It appears at this stage that this was an unfortunate plumber who was soldering in the roof space of a large building, which was undergoing total renovation," he said.

"For reasons we don't yet know, the fire has flashed up quickly and gone through the whole of a brand new and very expensive roof.

"Our initial investigations indicate that it was not his fault the flames spread so quickly.

"We think a blowtorch may have set light to expanded polystyrene foam in the roof space.

"Investigations will continue but that seems to be the most likely cause at this stage."

The mansion recently underwent a muilti-million pound renovation to open as a luxury hotel this year.

A listed bulding, the mansion was used as a location for several TV programmes and films such as 'The French Lieutenant's Woman'.

The eight-bedroomed home is owned by greetings card magnate Andrew Brownsword.

A spokesman for Mr Brownsword believed that there was no malice involved in the incident.