Associated Press, 2007       LONDON, England - During World War II, medium Helen Ducan was convicted under an 18th century anti-witchcraft law and jailed by authorities who accused her of compromising Britian's safety,     Several hundred people have signed a petition asking for a pardon. The campaign has the support of psychic investigators of the 1691 Salem witchcraft trials in America. In those trials 20 people were convicted of witchcraft and executed. A full pardon for all of them came in 2001, this pardon will probably be completed by 2007..     In the 1940s, Ducan was a well known medium, and her clients included Winston Churchill and King George VI.     But she ran into trouble after telling the parents of a missing sailor that their son had gone down on the HMS Barham, a ship whose 1941 loss had not yet been reported to the public in hopes of keeping morale high.     Military authorities grew jittery as the war went on, paricularly fearing that plans for the D-Day landings of Allied forces in northern France could be compromised. They accused Ducan of endangering public safety.     In Janurary 1944, police broke into a seance in Portsmouth, in southern England, to arrest her and she was charged with "pretending to be witch" under a 1735 law.     Duncan was convicted and jailed for nine months in London's Holloway prison. In 1951, Churchill's government repealed the 1735 law, but her conviction remained. She died in 1956.