I pitched him a modern-day Twilight Zone show, which he loved, but felt might be a tough sell.

Other ideas got banded around. A cop show. A romance. He smoked some fags, I drank some coffee until eventually Paul produced a short six or seven page document from deep inside a drawer.

It was entitled Exile and he said "Have a read".

It was a film pitch. It was set in America. It was about US politics. I liked it, but it was hard to see how it could fit onto a British TV screen.

However, at the heart of it was an intriguing father/son relationship. I am obsessed by father/son relationships and they are a recurring theme of my work. I was hooked.

The story needed a complete overhaul and, over the course of a few weeks, I set about storylining what would become the new version of Exile.

Storylining means working out the story, in acts and episodes. I tried to keep to the spirit of that original document whilst allowing it to take on a life of its own.

After leaving university, I'd worked as a journalist for a number of years, so Tom's world was one I knew and understood.

Draft one of the script included a 10 minute sequence where we saw Tom in the world of Ransom magazine: his lifestyle, his attitude and, ultimately, his downfall.

The BBC felt, quite rightly, that this was redundant. So now the story begins when he gets in his car and drives back north.

From day one, I wanted John Simm to play Tom. Partly because he was perfect for the role, but also because he is one of the best actors of our generation.

Whether it's The Lakes or Life On Mars or Never Never, if you see John Simm is attached, you know you are in for something brilliant.

As for Jim Broadbent, well, what can you say? The man's a star.

I remember watching him in Life Is Sweet when I was a student and loving his performance as a seemingly carefree father of problematic twins, and now here he is saying my words.

As for the supporting cast, we have been tremendously lucky to get such brilliant actors as Olivia Colman, Claire Goose, Timothy West and Shaun Dooley.

The most difficult aspect of Exile, without question, was dealing with the Alzheimer's.

I've written about illness before so I understand the importance of getting it right.

I threw myself into research, as I wanted a realistic take on what it's like to live with someone who is in the middle stage of the disease - when their mind is deteriorating but at times, still accessible.

I think I got it right but, to help matters, our producer Karen Lewis, our brilliant director John Alexander, and Jim Broadbent himself, all have first hand experience, so collectively we have brought a breadth of knowledge to our depiction of the disease.

Despite dealing with huge themes, I always wanted Exile to be more than just a thriller. I wanted it to be funny and characterful and quirky.

All the shows I have loved over the years - Cracker, Our Friends In The North, State Of Play - have managed to combine serious themes with light relief.

So, for me, the scene where Tom hides from Mike in the supermarket and ends up having an argument with Spotty Shop Assistant is a very pleasing scene. It symbolises my ambitions for the drama.

My personal philosophy is to try and write entertaining, contemporary drama that speaks to people about their lives.

But more than that, I want to write drama that if I was a viewer, I'd want to watch too. So... modern day Twilight Zone anyone?

Danny Brocklehurst is the writer of Exile.

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Comments made by writers on the BBC TV blog are their own opinions and not necessarily those of the BBC.