It was the mid-Sixties. Hegarty had joined the agency, Benton and Bowles, 18 months earlier as an art director. He had originally mapped out a career as a graphic designer, having studied at the London College of Printing. But it was there that he was a shown an ad by his tutor which changed his life. It was a VW ad by DDB.
"It was like a light being thrown on in a darkened room. I suddenly thought: 'this is brilliant, this is what I want to do'."
So he became a junior art director, but found the agency a little too restrictive for his creative energies. So they got rid of him.
"I think it was because basically I was a pain in the arse. Which is patently true. I was," he admits.
He then joined a small agency, John Collins & Partners, because he thought they were going places. They were. To Camden. Hegarty, of course, wanted to be in the hubbub, the epicentre of advertising, so he looked elsewhere. He joined the Cramer Saatchi consultancy which became Saatchi & Saatchi in 1970. A year later, he was made deputy creative director.
Recognising that the money men would come to dominate Saatchi's as it grew into the largest agency group in the world, Hegarty fled and went on to co-found TBWA London as creative director. There he met account man Nigel Bogle and planner John Bartle.
"We had a feeling we could do it better ourselves. That's not to be critical of TBWA - we had an idea of how we wanted to do things. That idea centred around a fantastic strategy closely allied to a great creative execution."
So in 1982, BBH was born and the idea proved an instant success. After four months, the agency had billings of over £6 million and a client list to die for: Audi, Whitbread and Levi's.
Hegarty was at the helm of ground-breaking work for Audi with the "Vorsprung durch Technik" campaign, while for Levi's, he created one of the most famous ads ever - 'Laundrette', which broke the mould by bringing a distinct visual style to advertising. The use of a Marvin Gaye classic also paved the way for a more innovative use of music in ads.
Thirty years on, BBH retains these clients and continues to produce award-winning work. It has been Cannes Advertising Festival's Agency of the Year twice, and last year was runner-up in Campaign magazine's Agency: of the Year awards.
BBH is currently "firing on all cylinders", as Hegarty puts it, with recent work making the headlines and impressing the awards juries once again: Levi's 'Twist' and 'Odyssey', Microsoft Xbox and the new Boddington's campaign are all examples of the strong creative output of late.
Hegarty attributes this to cyclical factors - what goes up must come down - and also to the nature of the staff, who he describes as 'leftfield', indicative of BBH's iconic Black Sheep.
On the tape, Hegarty, discusses what makes great creative, whether or not he lives up to his reputation as 'advertising's Mr Nice Guy', and responds to the dreaded question: "Where do see yourself in five years?"