Sir Martin Sorrell called me “a germ carrier”. A liar. A disgrace to the Financial Times. Then, a couple of days later, he invited me to lunch. Surely some mistake? “I actually checked before writing,” said his aide. “Can you suggest some dates?”

Our quarrel was over an interview in November. It was one of many that Sir Martin has given blasting the “bozos” at WPP, a maker of wire shopping baskets that he took on a 33-year odyssey to become the world’s biggest advertising and marketing services group — before his acrimonious departure two years ago.

Sorrell is still livid about his exit and, when we spoke last month, he went further than usual: calling for the head of Mark Read, his former protégé and successor as chief executive. But after WPP’s biggest investor criticised the 75-year old’s “disgusting” campaign to undermine his old company, Sorrell decided that his remarks had actually been off the record. A volley of bad-tempered emails followed, rolling into the night.