“I rang Charles yesterday and told him you were interviewing me...” (that’s Charles Dunstone, boss of Carphone Warehouse) “...and he said, ‘don’t tell him all the little things you do because you’ll look risible’.”

Sounds intriguing.

“And he also said, ‘unlike your friends on Campaign magazine, Johnny, who write that you are a jolly good bloke, he might work out what you’re really like’.”

Ooh, even better.

Hornby beams a golden, blokeish smile. At moments like this, when you are centre of his attention, there is no finer warmth to bask in.

He knows how to flatter, as you might expect from an adman currently rated the smoothest act in adland, but undercuts it with a chatty line in self-deprecating wit — just in case you might think he is a bit full of himself.

He has every reason to be. Last month Hornby’s agency CHI, set up two and a half years ago with partners Simon Clemmow and Charles Inge, won agency of the year in the British Television Advertising Awards. Last week it launched the first commercial in a huge campaign for his good friend Dunstone’s Talk Talk phone service.

In its short life, CHI has won business from big spenders such as British Gas, Heineken, Tango, Safeway, BT (which it gave up because of the Talk Talk launch) and Telegraph newspapers. It is a growth spurt that’s unusual even in an industry where flavour-of-the-month “hot shops” bloom and blossom with regularity.

Not bad for a self-titled “short posh bloke” who went to Marlborough school and worked his way through three big agencies before handling the Labour party’s advertising at the last general election.

And that’s just the start of Hornby’s connections: son of a Thatcher-knighted industrialist, best mates with Dunstone, close to Peter Mandelson (who sits on CHI’s board), half-brother of the writer Nick Hornby. Another novelist, Robert Harris, is married to his half-sister, Gill. He appears to have all avenues covered.

“He has that chameleon character,” says one of his friends. And all at just 37. Little wonder people talk of Hornby as a possible Maurice Saatchi for the Blair generation.

Sitting in a meeting room munching sandwiches at CHI’s base in Soho, London, Hornby wears his ambition lightly. Chunky, blond, handsome, dressed in a blue Richard James suit and open-neck shirt, he puts his agency’s rise down to the talents of his partners. The brains, he says, are provided by Clemmow (highly rated planner and former agency boss) and the imaginative spark by Inge (a former Lowe Lintas creative director and the man behind the Tesco slogan “every little helps ”).