The teacher, who has not been named, was an employee of Hillingdon education authority and had climbed to a height of more than 35ft when she fell as she began to abseil.

Her injuries caused the member of the National Association of Schoolmasters Union of Women Teachers to take early retirement.

Mary Howard, union legal secretary, said: “It’s a fairly high award but she is now unable to work and it takes into account loss of future earnings and pensions.”

Although a substantial award, the pound;475,000 payout is not the largest amount awarded to a teacher injured while working.

In January, a science teacher and member of the NASUWT, was awarded pound;562,538 after a carbon monoxie leak left him unable to work. John Gill was exposed to the lethal gas over a number of years while working at Royal Manor School, a secondary in Portland, Dorset.

In a separate case, another NASUWT member has won an eight-year fight to clear his name. Peter Cunningham brought a libel action against Essex County Council, resulting in a 10-day hearing in the High Court.

Mr Cunningham was awarded pound;9,500 damages and most of the pound;200,000 costs in the judgment.

The dispute centred on a letter written by the headteacher of a school at which Mr Cunningham had taught science until 1991.

Although the head had not intended the letter, which referred to Mr Cunningham’s redundancy payments, to become public, the county council had published it to third parties in a “casual and unguarded manner”, the High Court ruled.