MANCHESTER - Alan Henning, a volunteer British aid worker being held by Islamic State (IS) militants, should be released unharmed, his wife said in a statement issued a week after his captors threatened to murder him.Henning, 47, was part of an aid convoy taking medical supplies to a hospital in northwest Syria in December last year when it was stopped by gunmen and he was abducted.He appeared in a video released by IS last week, which showed the murder of another Briton, David Haines. In it, a masked man said Henning would also be killed if British Prime Minister David Cameron kept supporting the fight against IS."Alan is a peaceful, selfless man," his wife Barbara said in a statement released via Britain's Foreign Office late on Saturday."When he was taken he was driving an ambulance full of food and water to be handed out to anyone in need. His purpose for being there was no more and no less."