“Well, I just felt I had a set of skills that wasn’t being used,” says Lars Norby Johansen, chief executive of Group 4 Securicor, explaining his flight from academia. “It didn’t really matter what I did as an academic, it lacked a closeness to reality.”

So here he is, two decades after ditching the high-flying university career, heading a newly merged company with 340,000 employees in 106 countries and overseeing interests in manned and electronic security, cash services, prisons, electronic tagging and more. Close enough to reality now?

He laughs. “I couldn’t think of a better job,” says Johansen. “We provide security for people in a world that is crying out for security. That’s the meaning of what we do, and it gives my life meaning.”

Johansen is, by any definitions, a curious fish. At 55, freshly arrived in London to take his place at the top of Group 4 Securicor, he finds himself not just one of the biggest employers in Britain, but also, as a professor of political science, one of the most academically overqualified bosses in the FTSE 250.

He has, however, left academia a long way behind. Sixteen years ago he took on his first top slot in business: chief executive of Falck, the Danish safety and security specialist best known for running privatised fire services.

That had a workforce of less than 10,000. Since then he has grown the business, as often by merger as acquisition — first across Europe, then into America. Falck merged with Group 4 in 2000, bought US-based Wackenhut in 2002, then tied the knot with Securicor this summer.

That created a near-£4 billion- turnover giant that is now the world’s second-biggest security business by revenue (behind Swedish-owned Securitas). In the process Falck, the booster rocket to Johansen’s steady ascent, has been peeled off, leaving him as boss of Group 4 Securicor while retaining chairmanship of his old firm. He seems to have all angles covered.

And last week, as he surveyed the citadels of the City for the first time and reported Group 4 Securicor’s initial interim figures (pre-tax profits up 10% pro forma to £94m), he probably had more reason than most to smile. As part of the merger deal, Johansen agreed to move his Group 4 headquarters to a new base here. Having conquered Denmark, like any good Viking, he can presumably take the UK in his stride.

“The British are quite similar to the Danes. There’s a cultural understanding behind the language,” he says. “And my background, coming from a small, adaptive country, also benefits me.”

Sitting in a meeting room at his PR firm’s City base, dressed in a soft black suit and stripey tie, his grey hair cut long, and exuding the quiet reassurance of a relationship counsellor, Johansen looks and sounds like the least confrontational of bosses — an appearance that is undoubtedly deceptive, as you don’t build the world’s No 2 security empire just by being cuddly.

But his arrival is going to throw up some interesting contrasts in style at Group 4 Securicor, not least balancing the Danish preference for consensus with the more hierarchical British approach to running big people businesses. Then there is the intriguing matter of executive succession. As part of the merger deal, Securicor’s 43-year-old chief executive, Nick Buckles, becomes deputy chief executive of the new entity with a promise that he will take the top slot when Johansen steps down. And when will that be?

Johansen simply raises his eyebrows. “Nick has to succeed me at the appropriate time. It’s written into the merger and it reflects the fact that it’s a merger of equals. But at the end of the day it all depends on performance.”

Times Recommends

• C&G axed - 1,660 jobs to be lost
• UK house prices rise 1.1% as buyers return
• Mixed reaction to US banks repaying bailouts