The sketch shows Gandhi writing with a look of intense concentration whilst seated on the floor.

A previously unknown pencil portrait of Mahatma Gandhi, drawn from life and inscribed by him in 1931, was auctioned in London on Tuesday for 32,500 pounds, about four times its estimated price.

In addition to the portrait, a collection of handwritten letters by Gandhi to the family of Sarat Chandra Bose, a freedom fighter and the elder brother of Subhas Chandra Bose, fetched 37,500 pounds at a Sotheby’s auction.

“Gandhi usually refused to sit for formal photographs, let alone a portraitist, making this an extremely rare portrayal of the political leader at work,” the auction house said in a statement.

The sketch shows Gandhi writing with a look of intense concentration whilst seated on the floor, and is inscribed by him with the words “Truth is God/MK Gandhi/4.12.’31.”

The pencil drawing is one of a number of portraits created by artist John Henry Amshewitz when Gandhi was visiting London for the Round Table Conference in 1931, a series of conferences organised by the British government to discuss constitutional reforms in India.

Gandhi stayed at Kingsley Hall at the time, a community centre in London’s East End, at the invitation of one of its founders Muriel Lester who had previously stayed in Gandhi’s ashram (hermitage) in India.

The pencil portrait, which was inscribed by Gandhi the day before he left Kingsley Hall, was given to a local resident who was closely associated with the hall throughout her life and has remained in her family ever since.

In one of the letters, Gandhi writes to Sarat Chandra: “You should give up the struggle for unity of Bengal and cease to disturb the atmosphere that has been created for partition of Bengal”.

The portrait was estimated to fetch between 8,000 and 12,000 pounds while the letters were valued between 23,000 and 33,000 pounds.