‘The idea of being a cool London boutique agency was certainly a tag for a while,' he admits carefully. ‘But I think now people should look at the financials - it does show you can be creative and run a very tight ship as well.'
The financials - £4.38m of fee income in 2007 - are indeed healthy, as is the reputed £12m (disputed by Mathieson) he and partners Mark Whelan and Adrian Pettett will make from the recent sale of the agency to French group Havas Media.
A colleague is walking into a meeting with Carling clients but turns to hold aloft PRWeek's league table of top 30 consumer agencies triumphantly. ‘We're at number seven!' he yells to Mathieson, unaware of PRWeek's presence. And with greater emphasis: ‘We're higher than Frank!'
As we retire to the local café, Mathieson says he views such lists as ‘a load of bollocks'. But he has every reason to feel content - he clinched the Havas deal just weeks before the April tax changes.
Mathieson, 43, formed Cake in 1998 with Whelan and Ben Jones (who left to become a commercials director at Partizan), naming the agency after a sketch in Chris Morris's comedy series Brass Eye. Morris stirred up controversy about a non-existent drug called Cake, fuelling questions in the Commons.
‘We loved the idea of pulling the wool over the eyes of the media and the public alike. Of course, the client reason for the name is that a cake is multi-layered...'
Cake's special brand of live events has proved quite a draw for clients. The past few years have seen the agency turfing over Trafalgar Square for Visit London and holding a Faithless gig in the Arctic Circle for Lynx.
THQ International European PR manager Simon Watts worked with Mathieson for three years at Cake, helping to launch the Nintendo Wii. He says that one of Mathieson's key skills is his ability to make clients believe in him. ‘He was very good at selling an idea. He has this level of authority about him that people listen to what he says.'
The sale to Havas was announced along with news that the agency plans to open a New York office, something Mathieson is very excited about. He says he has had about 20 meetings with Havas' various companies in the past month.
So, why Havas, home of Biss Lancaster and the rest of the Euro RSCG stable? He makes a highly creative analogy to explain the move: ‘I would say that where WPP feels like it's cocaine-fuelled, Havas feels like it's sherry-driven,' he smiles. ‘We just felt we clicked with Havas really well. There's nothing like Cake in it's organisation, so we don't feel like a trophy purchase.'
He downplays the sum set to head toward his personal bank account as a result of the deal, claiming it is ‘less than £5m'. He adds: ‘Of course money is important, but it has never been about the money. It's about having a bigger playing field.'
Mathieson and his partners have a five-year buyout period, over which the cash will be spread. Once that ends, will Mathieson retire to his house in the country and live the good life? ‘I don't think of that as the exit moment for me. I'm enjoying this new world and who knows what the Havas group will offer us, particularly in the US.'‘
He ponders the suggestion that such a lengthy buyout could be dangerous. PRWeek refers to one agency that had a similar deal but whose directors lost interest way before the five years was up. Their apathy spread like a virus and the once-thriving agency started to sink.
‘You have to be very careful about that. I think the difference is that we weren't looking to sell the company like a fire sale. We weren't getting bored, we weren't getting to the stage where business was down.'
Mathieson's pre-Cake career saw him ‘bury the careers of Nick Heyward and the Thompson Twins' as a music PRO before starting his own agency named For Further Information.
Mathieson retains the down-to-earth good humour of a man with a music industry background. Not for him the stand-offish distance from the action of some agency heads - he clearly enjoys rolling up his sleeves. He is also disarmingly honest.
‘I have made every mistake in the book - bad hires, bad rental agreements, terrible financial decisions. I have this presentation called "danger notes". It includes things like what not say in an email when you're pissed off. Every single mistake in that presentation has been made by me.'
He says he is better at delegating these days, but probably less tolerant. ‘I think that comes with having children [he has three]; you want things to happen more quickly.' His thick skin, he concedes, can sometimes be a problem for others.
His passion for PR remains untainted, however. He talks of his ‘grim determination' over the years to have PR taken seriously as part of the marketing mix.
Mathieson paints a picture of a 19th century dinner party where guests represent advertising, direct marketing, PR and all the other marketing elements.
‘It comes to the end of the evening, and the host turns to advertising and direct marketing and everyone apart from PR and says "Shall we go to the other room and have coffee and leave the girls to it?" Well, I've always said I've got just as much right to be in there as anyone else.'
1998 CEO, Cake
1990 MD, For Further Information
1988 Head of promotion, Virgin
1986 Head of TV and radio, Polydor
1986 Radio promotion manager, Arista
1985 Regional radio plugger, Stiff Records
What was your biggest career break?
Starting my own business. Leaving Virgin at 25 as head of promotion, I was at the top of my game in the music business. But out on my own, I found I was good at self-motivation.
What advice would you give someone climbing the PR ladder?
Use your creativity - if you're a creative person, in our industry, you will go for miles. And network - I did so much networking. I'd be out every day and night, taking TV producers out. You can never have a black book full enough. Having good intuition is useful as well. It's a really important skill in our game.
Who was your most notable mentor?
Alex Johnst on, Freuds founding partner, who is now a partner at Fleming Media. In the past five years he's been someone to whom I can always turn. For me, it has become more important to have someone like that as I've become more senior. Someone I can turn to when I think ‘how do I deal with this situation?'
What do you prize most in new recruits?
People who show the power of creativity. I feel very proud when ideas are used that haven't come from me. Also the initiative and ability to juggle plates is important. It's quite a specialised skill. It is quite difficult to work on five or six clients at the same time.