Helen Duncan was tried under the Witchcraft Act

Medium Helen Duncan, who was born in Callander, Perthshire, was imprisoned using the law during World War II.

She was targeted by the government after revealing to a séance audience that a warship had sunk before the news had been released to the public.

Her grand-daughter is particularly angry at the accusations of treason.

Mary Martin, of Edinburgh, said Mrs Duncan had been accused of being a traitor.

Spiritualist churches

"When she first came back home after prison she was never the same.

"She always had a bit of a glow about her but she seemed to have lost that.

"Some people said it was treason. My grandmother had two sons and two son in laws in the forces ... and there is no way she would have given anybody information."

Mrs Duncan became one of the most famous mediums of her time. During the war she lived in Portsmouth, the home of the Royal Navy.

She has put us on the right side of the law by bringing in the 1952 act

Mary Armour

Medium

At a séance in 1943 it was claimed that the spirit of a sailor from the HMS Barham appeared.

The vessel was only officially declared lost several months later.

She was arrested in 1944 and sentenced to nine months in prison at the Old Bailey for crimes under the Witchcraft Act of 1735.

The Witchcraft Act was repealed in 1951 and three years later spiritualism was officially recognised as a religion.

Campaigners to pardon Mrs Duncan have set up an online petition.

The campaign has been backed by the British Society of Paranormal Studies.

Medium Mary Armour, who wrote her biography, said: "She has put us on the right side of the law by bringing in the 1952 act."