A blaze that severely damaged a dormitory at the historic Stowe public school led to a claim of £200,000, according to insurer Ecclesiastical.

The fire is believed to have been caused by an electrical fault in the roof. Flames spread rapidly, completely destroying the roof and causing severe smoke and water damage throughout the rest of the three-storey building, designed to accommodate 60 pupils.

The destruction would have been worse had the fire not been spotted by a group of boys, including Mick Jagger's son, James, aged 14, who swiftly raised the alarm.

Ecclesiastical said the building is now watertight following complete replacement of the roof. The study bedrooms on the ground and first floor were completed in time for the start of the new school term on September 12 – just three months after the fire happened.

The whole project will be finished by October 13.

Stowe, near Silverstone, Buckinghamshire charges fees of £15,000 a year and boasts many famous old boys, including Richard Branson, David Niven and Gorge Melly.

An Ecclesiastical insurance spokesman said: “Everyone was delighted the repairs were done so quickly - except, I suppose, the pupils who thought they could stay off school.”

The insurance was brokered by HSBC Insurance Brokers.