“I said I don’t do personalised numberplates. I think they are appalling. They’re not going on any vehicle I drive.”

Then whose souped-up, black Jag is sitting outside the front door, RHM1 proudly on the plates? McMahon, a 52-year-old, hard-nut Scot, suddenly looks sheepish. “Er, that’s mine,” he says. “My wife pointed out that if I visit a plant and I don’t have them, people might think I’m not proud about doing the job.

“And she knew exactly what I would do here, lots of painful change, lots of anxiety. Her counsel was: you don’t need to make a public statement by ditching the numberplate as well. It was a classic case of where intuition is right. That’s what my wife does.”

And a bit more. McMahon’s wife has only just stepped down from a senior job at ICI, where he used to work, too. But since 2003 he has thrown himself into RHM, the food giant that numbers Hovis, Bisto, Mr Kipling and Sharwood’s among its brands.

True to his wife’s prediction, he has swept through the firm, removing more than half of the top 50 executives, closing plants, rewriting pension options (to plug a £520m pension deficit) and restructuring business units.

The fruits of that ruthless reorganisation were seen last Tuesday when RHM, previously owned by private-equity group Doughty Hanson, was floated on the stock market and immediately soared in value, despite analysts’ fears that future growth might be hard to come by.

That same morning, Kirkcaldy-born McMahon, whose reputation as a charming but tough troubleshooter was honed at GrandMet, sold 500,000 of his 2.5m shares, making himself a cool £1m in the process. The Jag parked outside RHM’s base in Marlow, Buckinghamshire, could soon be upgraded.

He shrugs when I bring it up. “I know this sounds trite, but money was never why I came here.” He just likes sorting out companies. “It’s what I do.”

Sitting in his impossibly tidy white office — just two jungle plants and an orchid for decoration, no pictures of family, no RHM products — McMahon can, at times, seem slightly intimidating. Compact, pin-neat, softly spoken, with the pouchy good looks of a mid- period Sinatra, he exudes serious determination, leavened with only occasional dry humour.

So where are the cakes?

He doesn’t blink. “Och, there’s normally a selection over there,” he says, nodding towards the door. “They must have heard you were coming.”

But he knows how to reorganise a company; that much is evident from a CV which shows him heading overseas subsidiaries for Tootal textiles at 26, revamping Pillsbury’s UK food interests for GrandMet, and overhauling ICI’s European paints division.

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