Smiling, in his crisp white shirt, Hegarty at once appears to bear out his reputation of "Advertising's Mr Nice Guy - a tag with which he is not entirely happy. "I read that once somewhere and I thought, 'God, what an awful bloody title to have!', he says.
Is it simply a case of good brand management, while all the time there is a ruthless streak lurking beneath the surface?
"I've always tried to be fair with people, to be straight and honest with them, he responds. "I've always loved the creative people because they're the ones who are confronted with the blank page.
"But I do believe it's the hardest department in the agency and one of the toughest things you have to do is to say to people you're very fond of 'you've got to move on'. I do find that very difficult."
BBH is undergoing something of a creative rejuvenation, as recent awards ceremonies have proved, so hiring rather than firing is the order of the day. And although it could be argued that there is a trademark BBH style, all of the new work, whether for Levi's, X-box, Boddington's or Barclays, is as distinctive within the agency as it is within advertising itself.
Hegarty partly attributes the recent good fortune to cyclical factors; to those rare moments when it all comes together at once, be it new-business opportunities, or the fact that a campaign is coming to a natural end and needs a new voice. But he also points to the agency's traditional emphasis on attracting the best talent. The French creatives Fred & Farid are among the latest hirings whose work is causing a stir within the industry, with many tipping their simple, daring and bizarre X-box campaign for success at Cannes.
BBH has also had a tradition of discovering and promoting new directing talent, particularly as far as Levi's is concerned. However its most recent work has been executed by established directors, including Jonathan Glazer and Frank Budgen. The pressure to come up with something new and exciting may have led to the use of younger directors in the early days of Levi's advertising but as established directors began to take a more innovative approach to scripts, the agency drifted back to using them. According to Hegarty, though, the change is also the fault of the young directors themselves.
"It was interesting with 'twist' the number of directors who turned it down - because they didn't have the courage, he says. "So often, directors say to me, 'there are no good scripts out there'. Then you give them a daring script and they say, 'I'm not sure I can do this'. So it's not surprising that they're sitting there not making the breakthroughs."
Despite this, BBH remains committed to looking beyond the tried and tested.
One initiative recently introduced by the agency is "Mint Source - a compilation of work from new or low-profile directors. Initially intended as an internal resource for creatives, it will now be made available externally.
It will also feature on a New Talent issue of Campaign Screen in October.
The Mint Source team is also aiming to get promo commissions from record companies to give its own creatives, as well as new directors, broader creative opportunities.
There are other new ideas on the horizon, including a move into programming, products and even a record label. Hegarty believes now is the most exciting time to be in advertising. "We can cross over into all kinds of media and for the first time are being taken seriously by other industries. It's a tremendously important opportunity for us, he says.
For this reason, Hegarty claims that BBH's ambition is not to be the most creative advertising agency in the world, but "the most creative company in the world".
As far as his own ambitions are concerned, Hegarty is less certain: "I don't have a five-year plan. My mantra is 'do interesting things and interesting things will happen to you'. I don't know where I'll be in five years. I don't want to know."
You can watch this interview and more on the current issue of Campaign Screen.