It’s a cold, clear winter day, sunlight streaming into the upper floors of Clifford Chance’s palatial head office in Canary Wharf, in east London. The firm moved out here in 2003, breaking away from its rivals in the Square Mile, and now happily keeps company with major clients such as Barclays, Citigroup and Credit Suisse. It makes sense: for all the strides it has made in other areas, the world’s biggest law firm is still led by its banking and finance practice.

Mark Stewart, 49, managing partner for London finance, is the public face of the practice. His is also the sort of personality the firm wants to project: driven, hard-nosed, but less stuffy than the other, longer-established “magic circle” firms.

A garrulous north Londoner who grew up in gritty Holloway, the son of a high street solicitor, Stewart is the first to admit he is not the most intellectual of lawyers. “I don’t think I’ve read any fiction since leaving school, much to my eldest daughter’s disgust,” he says.

He also claims, wryly, to be the only finance partner at Clifford Chance who has never drafted a loan agreement. (He acts mainly for corporate and private equity borrowers rather than for banks.) But such self-deprecating remarks belie a reputation as one of the City’s shrewdest, most combative finance lawyers.

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The past few years have been good to Clifford Chance. Last year, it earned £1.2 billion — more than any other law firm in the world — with equity partners taking home, for the first time, an average of more than £1 million. Such staggering profits will be difficult to sustain with a downturn looming, but Stewart is confident that Clifford Chance will benefit from a flight to quality as the market contracts.

“The market as a whole is going through a slightly quieter period,” he admits. “We’re not immune to it and we have to work harder to get the work in, but we don’t get so affected. Since I became a partner [in 1990], we’ve never had a quiet spell.”

He points out that the London banking practice has advised on more than 135 billion euros in loans since September, despite the turmoil in the financial markets.

This is not to say Clifford Chance takes success for granted. The youngest of the “magic circle” firms (it was formed by the merger of Clifford Turner and Coward Chance in 1987), it can’t boast Freshfields Bruckhaus Deringer's historical ties to the Bank of England or Slaughter and May's deep relationships with the titans of industry. That has produced a sense of insecurity — a feeling, as Stewart puts it, that “there are others that are slightly better than us”.

Such fear produces a galvanising effect. Outwardly, Clifford Chance has been criticised as something of a factory, too vast and impersonal — in 2002, it ranked dead last in The American Lawyer’s annual survey of associate satisfaction — but the culture Stewart describes is one of teamwork and inclusiveness.

The partners are less obsessed with individual relationships than their rivals, he says. There is little tolerance for “big bulls”, for the sort of domineering personalities “who are rude to the secretaries or indifferent to the IT people”.

Rather, he says, they have learned a painful lesson from the merger with New York firm Roger & Wells at the start of the millennium. He explains: “The other firm was dominated by some very big characters, big-hitting individuals who were great while they were there, great for themselves, but were creating a culture that was fairly destructive. The whole New York exercise convinced people at all levels that you’ve got to stick to the principles and ethos beyond short-term potential gains.”

As if to prove this collective spirit, Stewart and another partner recently took their families on a quad-biking trip to Mexico. In April 2006, he and two other finance partners walked to the North Pole, raising more than £1 million for various charities.

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