It is understood the APPC has approached Butler with a view to him heading up its Professional Practice Panel - previously called on in 1998 to investigate agencies embroiled in the 'Drapergate' lobbying scandal.
The APPC is resurrecting the panel of heavyweights to investigate claims that Morgan Allen Moore chairman Steve Morgan breached its code of conduct while working on Peter Hain's Labour deputy leadership campaign. Morgan strongly denies any wrongdoing.
The claims were first made by a former employee with links to the Conservatives.
Butler has served five prime ministers: Heath, Wilson, Thatcher, Major and Blair. He recently headed the inquiry into intelligence behind the decision to go to war with Iraq.