How do you feel about Guilt coming to an end?

I definitely feel sad, and already nostalgic, if you can feel nostalgic for something that’s not quite finished. But at the same time I’m very happy with the decision to bring the show to a close with this series. I think the story has come to a natural end, and we are finishing strongly without outstaying our welcome.

Did you know from the start where the brothers would end up and where their story would go?

I didn’t even know what was going to happen after the opening scene of episode one, let alone 12 episodes later. But I knew the characters and the worlds I wanted to send them into, so hoped the story would come. And the ending that I reached felt both surprising and inevitable, like all good endings should.

The three themes of Guilt are guilt, revenge and redemption... can you tell us a little more about that?

I like running that unifying thematic thread across characters and stories, though you have to be careful not to overdo it. Specifically those three themes felt like natural progressions within a trilogy, each one reactive to what came before.

The last series was complex and layered, with several different storylines interwoven. Can the strands all be tied up for last in the Guilt trilogy?

I like to think that this series ties up strands from both the first and second series, which was hard work but hopefully I managed it. I definitely think you have to give a viewer who has stuck by you over three series a satisfactory ending for as many of the characters and storylines as you can. Knowing this was the final series, and that being my decision, helped a lot. I didn’t have to leave anything open to hopefully get another series, I could concentrate on closing things down.

Jake and Max are treading water as this series starts. Without giving anything away, do they both begin to get a sense of purpose other than survival?

Yes, they both reach a stage where they don’t just want to stay alive, but they want a better and different life. They are old enough to realise that something needs to change - whether that’s something they can choose or is foisted upon them. They also realise, I think, that they can operate independently of the other - physically and psychologically.

The first episode opens with a high-octane scene, where a young woman puts herself in a dangerous position. It doesn’t end well. Have you introduced new blood to this series?

Yes, one of the really fun things with Guilt is bringing in new characters and finding brilliant new actors to play them. There are some fantastic new actors in this series who I think have blended in seamlessly with the quite specific tone we try to hit with the show.

There are returning favourites coming back for series three. Which character/s do you have a soft spot for? All of them have shades of grey but are there some you root for more than others?

I was delighted to bring a number of characters back, but the prospect of Ellie Haddington (Sheila) returning was in my mind from the moment I started writing the story of this series. The important thing is that you are not bringing people back for glorified cameos, you need to bring them back with a real narrative purpose accompanying them.

The last series unravelled the story behind gangster Roy Lynch and that his (supposedly ex) wife Maggie wasn’t who she seemed. Now with Maggie at the helm of the organisation, how will this new relationship with the brothers develop?

I love watching Maggie and the brothers together, there’s an oddly maternal aspect to their conversations, despite the subject matter. They both seem automatically cowed in the presence of a stern older woman, which I think is quite an East Coast Scots thing.

With a raft of awards behind Guilt, was there a certain pressure to deliver on the promise of this final series?

No, I couldn’t think like that or I’d risk second guessing myself. I just had to take my usual approach, which is write an entertaining story driven by interesting characters. My test with any script is, why is the viewer still watching this after 10minutes? While I like to think I write stories with a bit of craft in them, I don’t forget that television should ultimately be entertainment.

How important has humour been in the writing? Dealing with dark subject matter doesn’t always lend itself to comedy. Was this a difficult balance to strike?

I see humour as a vital part of the dramatist’s armoury and I’m always confused when it’s not used. A drama that runs for six hours without anyone saying anything remotely amusing is, for me, completely unrealistic. Humour is one of the main ways that human beings react to pressure, threat and fear and if it’s absent then I think that detracts from the show. I never force it, and I don’t make story choices to set up funny lines, but if it feels to me that the character in that moment would say something that is funny, then that’s great and in it goes.

What do you think Max and Jake really want from each other in the end?

I think they both want the other to let go of whatever hold they have on them. I think they want to be respected by the other, for their qualities to be occasionally recognised – to go with the very regular appraisal of their flaws. I think they want to see more of what they love in the other, and less of what they detest. I think they want to find some peace and, at some level, they both think the secret to finding that peace lies with the other.

And if you had to be one of the brothers, which one would you be and why?

Jake, but just for the hair.

What can fans expect from the third and final instalment of Guilt?

I hope they can expect a good story, a chance to see the characters be driven to new depths of emotional discovery and desperation and an ending to the Guilt story that they are happy with. And over the years I hope we’ve offered some entertainment and escape from life’s travails.