Frances Shand Kydd left her home on the Isle of Seil, near Oban, at the beginning of the week to travel to London.

She appeared at the Old Bailey on Thursday to give evidence in the trial of Princess Diana's former butler, Paul Burrell, who has been accused of stealing hundreds of the princess's personal items.

The break-in was discovered on Thursday morning by her housekeeper.

It included items of value and, more importantly, sentimental value, pieces which belonged to my grandparents and a ring given to me by my father

Frances Shand Kydd

Mrs Shand Kydd, 66, said the telephone line had been cut and the house ransacked in a burglary that appeared to have been carried out by professional thieves.

She said: "While I was away giving evidence my house was burgled and all my jewellery taken. Everything.

"The house is a tip. The wires of the phone were cut, and the security system."

The items, said Mrs Shand Kydd, were of great personal value.

She said: "It included items of value and, more importantly, sentimental value, pieces which belonged to my grandparents and a ring given to me by my father.

"They went through the entire house. Nothing pertaining to Diana was taken. They were professionals looking for jewellery, which they took."

Mrs Shand Kydd has lived on her own at her Argyll home for many years and her presence at the Old Bailey was a rare public appearance.

A spokeswoman for her son, Earl Spencer, said: "It is dreadfully sad but now it is a police matter."

During her evidence, Mrs Shand Kydd revealed that she and her daughter had a tempestuous relationship and Princess Diana had not spoken to her mother for the last four months of her life.

A spokeswoman for Strathclyde Police said: "We can confirm that police are investigating a break-in at Clachan Seil.

"Items of jewellery have been reported stolen and enquiries are ongoing."