According to Tesco legend, Terry Leahy was identified as chief executive years before he eventually got the top job at Britain's biggest supermarket group.

Lord MacLaurin, the man who transformed Tesco into a stores chain the middle class was prepared to shop in, spotted Mr Leahy early on.

"Before Terry was even an executive MacLaurin would point him out to people from outside as the man set to succeed him," said one person who worked with both men. "MacLaurin then did what any good chief executive is supposed to do and organised a smooth transition of power."

It is four years since Mr Leahy, now 45, became chief executive of Tesco. Last week he announced the grocer had joined the exclusive £1 billion sterling (€1.6 billion) retail club as its profits breached that barrier. It is, of course, the only member of the club since the sharp fall from grace of Marks & Spencer.

There was little fanfare. Making a big noise about record profits in food retailing while farmers are suffering would have been highly insensitive. A dignified explanation of profits combined with a staunch defence of the position of supermarkets was more the order of the day.

Anyway, triumphalism is not exactly Mr Leahy's forte. Serious and intensely private, he stands out in an industry where garrulousness is more the norm.

Famed for his single-minded focus on Tesco, Mr Leahy has worked for the group for 21 years. For such a long-time company man, Tesco has changed remarkably since his appointment as well as going from strength to strength in terms of profits, turnover and market share.

When Mr Leahy got his hands on the reins, the group had already overtaken its rival J Sainsbury to become Britain's biggest grocer and was widely regarded as a phenomenal retailer. But the group that pushed through the critical £1 billion profits barrier is not just the one Mr Leahy inherited. His time at the top has led to an even more fierce focus on value, more non-food goods, an aggressive push into online retailing and expansion into emerging markets overseas.

COLLEAGUES, rivals and analysts agree it is Mr Leahy, not Lord MacLaurin who can claim the lion's share of the credit. "A retailer is really only as good as its last two years, just look at Marks & Spencer," said an industry insider.

"Most of what you see today is Terry," said an analyst. "MacLaurin laid the foundations, but it is Terry who has carried it on."

A former colleague, now with a rival retail group, agrees that current and past managements deserve credit.

"Anybody today who doubts that the current success isn't down to a mixture of both and more recently down to Terry Leahy really doesn't know how retail businesses work," he said.

His management style is also sharply different from that of the more personable Lord MacLaurin. A quiet man, whose voice still shows his Liverpudlian roots, Mr Leahy often appears dull. He always chooses his words with care and rarely says more than is absolutely necessary.

"When he took over as chief executive there were people in Tesco who missed the dash and the style of Ian MacLaurin who very much wore his heart on his sleeve," said someone who used to work for him. "But most of those people have now become fiercely loyal to Terry because he has a plan, he communicates it well and he is single-minded in going for it."

Others say it was Mr Leahy's quiet manner that helped mark him out early as a high-flyer. "When you went to meetings in the MacLaurin days, Terry would always slip in just before they started. He would say very little but every single thing that he did say was absolutely to the point."

Many people put Mr Leahy's character down to his background, which is not that of a typical blue-chip chief executive. A working class boy from Liverpool, he won a scholarship to the local grammar school before going on to the University of Manchester Institute of Science and Technology.

There was no business background in his family, but he had worked stacking shelves in Tesco during one school holiday and went straight from university to join the Co-op. After less than two years he jumped ship to Tesco where he worked in a variety of marketing and commercial roles.

Many highlight his intellectual approach to business. Admired by his industry peers, Mr Leahy is widely regarded as the greatest retailer of his generation.

"Terry is a brilliant retailer, there is no other way to say it," said one. "He has a great mind and he understands his industry from the supply chain through to the customers as a scientist. But he also has an instinctive nous for it."

Once a retailer has become as successful as Tesco, the questions about longevity begin. Rivals admit they have little chance of catching Tesco, unless it makes mistakes. So how does it ensure it does not become the M&S of the future?

Mr Leahy says keeping a constant watch on the business is key. "We have watched and seen some of the things that have happened to M&S and to Sainsbury. When you have done that you know never to be complacent," he says. "Tesco also had bad times a few years ago, but it came through them. A good measure of a business is how it comes through tough times."

Still, many retail observers are keen to drawn comparisons between the Tesco of today and M&S's glory days under Sir Richard Greenbury. Certainly the management insularity and arrogance of the Greenbury years are, by common agreement, evident at Tesco today.

Both groups also rely on the strength of a corporate name that has come to represent everything its retail brand stands for. As M&S can testify, when things start to wobble under such circumstances, they can go badly wrong very quickly.

Those who know him well, however, say Mr Leahy would never allow himself to make the same mistakes as M&S.

"HE IS the antithesis of Greenbury; he doesn't bully, he never raises his voice," said one. "He makes his displeasure absolutely clear if you have dropped the ball. But he never loses his temper and he won't lose respect for people just because of one mistake."

Others say that while his personal manner is often offputting, he is a good listener. "He is one of the most reasonable men I have ever met," said a former colleague. "He always listens to advice. He doesn't always take it, but if he disagrees he will always go to the trouble of telling you why."

Others are less sure. "I'm not sure that Terry has surrounded himself with people who will challenge him enough," said one. "His interpersonal skills are not the best in the world and he is a bit of a cold fish. That puts plenty of people off."

Football is about the only subject certain to bring out the human side of Mr Leahy, a fanatical Everton supporter.