With Britain at war talk of treachery is often inevitable. But do we use the term too readily these days?
Two biographies out this month deal with some famous traitors. Lord Haw Haw by Peter Martland reveals the story behind the last man to be hanged for high treason in Britain during the second world war. The Greatest Traitor, The Life of Sir Roger Mortimer by Ian Mortimer is the story of the 1st Earl of March, the aristocratic rebel imprisoned in the Tower of London in 1322, only to escape to France a year later and ultimately force the abdication of Edward II in 1327.
Here, Peter Martland, Ian Mortimer and Yuan Potts of the Today programme profile some of Britain's most notorious traitors. Click on the images for more detail.