Almost a dozen passionate letters sent by Sir Mick Jagger to his secret lover in the summer of 1969 have sold for £187,250.

The price was more than double the pre-sale estimate of £70,000 to £100,000.

They were purchased by a private collector, bidding over the telephone.

The letters, said to paint a picture of Sir Mick as a "poetic and self-aware" 25-year-old, were written to American-born singer Marsha Hunt while the Rolling Stones frontman was in Australia.

Hunt, who provided the inspiration for the Stones' 1971 hit Brown Sugar, had tasked Sotheby's in London with selling 10 letters at auction.

At the time she was the image of Black is Beautiful and the face of the landmark West End production of Hair.

After the sale, Hunt said: "The passage of time has given these letters a place in our cultural history.

"1969 saw the ebbing of a crucial, revolutionary era, highly influenced by such artists as The Beatles, The Rolling Stones, James Brown and Bob Dylan.

"Their inner thoughts should not be the property of only their families, but the public at large, to reveal who these influential artists were - not as commercial images, but their private selves."

Dr Gabriel Heaton, Sotheby's books specialist said: "We are delighted with the result of today's sale which reflects the great significance of these letters, written at such a vivid moment in social and musical history."