To 50 Albemarle Street, former HQ for John Murray publishers, a powerhouse of British writers from Byron, Darwin and Disraeli to Walter Scott, Conan Doyle and Paddy. "Jock Murray was the best publisher and editor Paddy could have hoped for," says Cooper. "In the days before agents he was also Paddy's banker, therapist, PR consultant, book-finder and poste restante."

Picking up the pace now like horses heading home—drinks at the Travellers Club await—we stride magnificently down Jermyn Street. One imagines Paddy, sartorially something of a peacock, thoroughly at home here. 

"Oh God, absolutely!" Cooper says, laughing. "Hats from Lock, shoes from Lobb, Savile Row suits. He loved all these shops. Paddy adored clothes. In all his books the costumes of men and women are described in extraordinary detail. I've walked along Jermyn Street with him, striding along with his cane with that lovely flick upwards before putting it down. If you didn't know, you'd think he'd never left the Home Counties."

Into the final furlong and past the Cavendish Hotel, an unlovely blend of underground car-park and drive-through fast-food forecourt. "Here he met the tail end of the Bright Young Things, a decade after all those parties that had scandalised society." Alistair Graham, Jennifer Fry, Eddie Gathorne-Hardy, Mark Ogilvie-Grant . . . and Elizabeth Pelly, to whom Paddy lost his virginity. 

"They're a revelation to him. Godlike and irresistible. Suddenly he feels he's met kindred spirits." He didn't meet Evelyn Waugh at the Cavendish because Waugh was banned. Mrs Rosa Lewis, the owner, did not find her portrayal as Mrs Crump in Vile Bodies amusing. "If I get my 'ands on that Mr Woo-agh," she told Paddy, "I'll cut 'is winkle orff!"

Through St James's Square and we're almost trotting into Pall Mall, from where it is a hop, skip and jump up the 11 steps into the Travellers Club, whose bar Paddy did more than most to prop up—together with those of White's, Pratt's, the Beefsteak and the Special Forces Club—during 66 years as a member. In 1950, the Club Secretary reported to the House Committee that the nomadically careless Paddy owed "over £100 for storage, if by-law 6 were to be strictly enforced".