The best advice to retired executives who are thinking of criticising their successors is: don't. Carping former executives are usually seen as bitter, past-it and retrospectively attempting to justify their own records. Any merit in their criticism goes unheeded; people are too overcome by the stench of sour grapes to listen.

Recollections of Sir Edward Heath's time as British prime minister are not filled with affection or regard, marked as they were by industrial discord and national decline. But what really did for Sir Edward's reputation was his constant sniping at Margaret Thatcher, his successor as Conservative leader.