A former advertising copywriter with whom I’d worked on a few ad campaigns back in the mid '80s had contacted me out of the blue to request a 15 minute meeting.

I had just started a new job as CEO of Clear Channel, a company that designed, built and maintained street furniture - bus shelters, bins, public toilets - on behalf of Local Authorities across the UK, paid for by having the advertising rights on a proportion of the structures. Clear Channel was also one of the largest billboard companies in the world.

Martin Firrell was uncharacteristically nervous. He talked non-stop. About small words making a big impact. About wanting his words to be a force for good in the world.

He said he'd been working on ads without a client, and wanted to know how to get the ads shown on billboards when he had no client budget.

I remember cutting him short: ‘Those aren't ads. That's art. Public Art.’

I loved the work. I wanted to help bring it to a wide audience. And I thought maybe we could be a sort of ‘corporate patron’ of his art in the public domain.

Billboards are the perfect high-impact medium. The only truly mass broadcast medium left. You don't have to seek them out. They find you. They are designed and positioned to be visible. Unignorable.

At the time, we had just launched one of the UK's first high definition digital billboards in Leicester Square. It had an audience of over a quarter of a million people a day. There and then I picked up the phone to the MD of our billboard division and said I had a great idea to showcase the new technology and the impact of our signature screen.

Not pure altruism. Not a favour for a former colleague. A real potential win-win. Life is made up of just these 'Sliding Door' moments. A week later, Martin's work was up on the streets of London. And the rest, as they say, is history. A very different public artist was born. And, in Martin Firrell's own words, different is not wrong.