When I catch up with Mark Stringer in the uber-trendy Clerkenwell Road offices of PrettyGreen - his PR agency with a twist - it's the day after the company's 'summer conference'.

Strings, as he's universally known, is bearing up well considering he ended up at Camden Stables and was "asked to leave around 3am by the bouncers because I was doing pull ups from the roof". He managed his personal training session at 8.15am, and while he's feeling "battered" he's still a bundle of energy.

"I come to work because I like it and it's fun, I'm fortunate enough to have crafted out a job where I get paid for having fun…why would I come to work and not have fun? Why would I want to come into the office and not really love the space we've created?

"If I can get my team to work on the projects they love they don't care if they get up at 6am and go to bed at 5am because it's fun and it's enjoyable and it's a passion set. I say to everyone I just want you to do more of what you want to do and be more of what you want to be and if I can do that for you then we'll be a success."

The team is the 40+ staff he has recruited since starting the agency a little over four years ago, on July 4, after a decade at Exposure, the agency he helped build from a 10-man business into a £20 million company employing more than 140 people.

He left Exposure "to get out of the industry, I wanted to write a book, just do something different – create brands".

Red Bull was his first client and four years on the PrettyGreen client portfolio is a mix of start-ups, including the absinthe brand Strings brought to life (more later), alongside big consumer brands like Nando's, Cadbury, Under Armour, John Lewis, Electronic Arts (and a few others which haven't been announced yet).

He named the agency after a song on the Sound Affects album by Paul Weller and the Jam. Waving around a £1 note (which he kindly gives me to keep), Strings enthusiastically explains that 'pretty green' is slang for a £1 note.

"As a big Jam fan it resonated with me but I suppose I love the name - and we had it a year before Liam Gallagher took the name for his clothing label - because at the end of the day what we do is about cash and return on investment. Clients want to make a return, it's all about cash.

"But we're not wonga. I like the softness of it and the fact that you can have a conversation about money without it being harsh and aggressive. And there are other bits that play on the name - we don't know everything, we're green and I think it's a great belief to have."

Our meeting is timely as he believes that four years in, the agency, which is located in a warehouse-style building decked out with a sports room, a grass-covered recording studio and colourful murals with mantras such as 'manners cost nothing' scattered around the walls, is at a key point in its development.

"I think we're at a tipping point – we'll either be the agency that I think we can be or we’ll be mediocre. I think we're at that point, and if I listen to what people say, we're an exciting agency which has had phenomenal growth and we'll either be that agency that sort of nearly but didn't, but my view is that we'll be one of those agencies of note."

Strings created PrettyGreen originally as part PR agency/part incubator agency for brands wanting a launch pad. He was also adamant that he wasn't going to set up a traditional comms agency with all the trappings.

"I like the idea of always being a start up, or an upstart. I like the idea of always changing – so having new teams and new groups and splintering and not feeling like a big company that can't change and move and innovate."

Steering away from the usual agency model allowed him to indulge his ultimate passion – creating brands, and when an old acquaintance came along with a proposition to make absinthe, Strings jumped at the opportunity.

"We went to France and we didn't have a name, we didn't have a product, we didn't have anything and we made it from scratch."

La Maison Fontaine absinthe, launched two years ago, is now the most awarded blanche absinthe in the world and is found in Mandarin Oriental hotels, the Paramount Club, as well as being rolled out across more territories around the world.

"That's where the incubator changed slightly…the amount of time I had to put into this. There was only two of us – we wrote the business plan, we raised finances, got it funded, got investors, appointed distributors."

While he's still talking to start ups who need PR support, from food brands to juice brands, technology brands, sporting brands, he has tweaked his original "sweat equity" proposition.

"I very quickly realised that this agency is an incubator for the people who work here – we can create a music division (which launched in May) or a sports division because somebody here wants to. And we're looking at creating our own events because people want to.

"We've also got some really interesting conversations going on in the alternative sports scene about creating something there which I'm hoping we'll launch before the end of the year. Not because I want to do it but because there are people passionate about it. I'm just trying to unlock their passion set for the business to become successful."

Constantly driven by a "fear of failure", Strings has an unusual approach to helping his employees reach their potential.

"What I say to the people who work for me is 'my job is to hold your hood off the edge of a cliff and push you to do the things you don't want to do because afterwards you'll thank me'.

"It's easy to avoid something you're not very good at…just push, just push yourself a bit harder."

Every person in the agency has a bucket list and receives £100 a year to help them achieve something on that list. Mark has led the charge with a fire walk and others in the agency have tried their hand at hang gliding, making marmalade jam, singing lessons, a show on Broadway, and learning to drive to name a few. There is also an agency-wide competition to get £1 notes signed by interesting talent worked with, with the winner receiving a £500 bounty. Framed bills autographed by the likes of JLS, Robbie Maddison, Rob Da Bank feature prominently near a huge communal bar area.

While his original incubator idea may not have come off in the way he first imagined, his next big plan is launching a venture capital fund for the PR industry.

"Rather than have something that's all about sweat capital, I want to actually move into more investment. I think the agency is doing well, we've built up the reserves – for me it's about using the money to create brands.

"New brands and start ups break rules and they make a new landscape. When we started making an absinthe, they said it will never go into cocktails, it won’t work – but you do it because you don’t know anything different. Brands like Under Armour and Nando's have broken the rules and I like the idea that I can transfer that learning and that skill set.

"That's why I like the idea of the incubator and the VC fund, it feels instinctively right for me, it feels complementary to what we’re already doing."

And what about the future? "When it's not fun anymore I won't do it."

"At Exposure I got the nice house and the car and the watch but it was always a material trinket I was collecting as a way of saying I must be successful…I think the difference for me now is am I happier, am I having more fun rather than am I still collecting trinkets. I'm still materialistic to a point but nowhere near the same way that I was before setting up PrettyGreen."

His big hope is to do "great business with great people". One of the most recent additions to the agency portfolio is American apparel brand Under Armour.

"What has been fantastic is another client – maybe it's the way we do business or maybe it's our culture – just embracing the fact that we can do things that are different. They're the sorts of relationships we want and we want to spend time with clients because they're fun, enjoyable, like-minded spirits who want to make a difference.

"That's the fundamental reason our business has grown as quickly as it has done because we’re doing work with people we like and they’re enjoying the working relationship as opposed to 'they’re really good but I don’t really like them'.

"Hopefully whoever you meet in the agency you'll think they're really nice and that there’s a really nice atmosphere – clients work from here, you'll find clients dotted around the agency working and that creates a better relationship which hopefully gets us more work."

But for the moment he will continue to drive the business, do "amazing work", keep the upstart spirit alive and combat the challenge from ad agencies muscling in on the traditional PR territory.

"PR agencies are going to end up back where they were – as an afterthought brought in to amplify the idea. Now the ad agencies are saying they can come up with all these ideas and just get the PR agencies to talk about them.

"So the big challenge for the PR industry is own those ideas and demonstrate it is capable of delivering the ideas and the amplification because the only reason for coming up with the idea is to get the consumer to see it and hear it. We talk about the contentment model of harnessing existing ideas and creating our own content that gets it talked about – you put the two together and you have a campaign.

"PRs need to stop asking how do you get to the top table and just start eating – we just need to get on."

Strings was speaking to Celina Maguire, Consumer Editor.