You’ve been in Grantchester since the beginning, longer than you’ve ever been in any other series. What keeps you coming back?

As I'm in the last third of my life, I want to work with people I love working with and do projects that make me genuinely happy and push me creatively. But in the end, I just really want to have fun doing what I love. And Grantchester caters for those needs. I’m an executive producer, and at the beginning we knew we had something special and that would float the audience's boat, but we never realised how popular it would turn out to be and how well it would be received around the world. But as long as Daisy [Coulam] is at the helm, with [executive producer] Emma Kingsman-Lloyd and as long as we have cinematographers and lighting designers at the top of their game, and we’re all still enjoying it, long may it continue.

What sort of reaction do you get from fans?

I just came back from doing a fishing show in Australia. In the outback I was with what I’d call really stereotypical Australian blokes who run a cod hatchery, who told me Grantchester was their favourite show! It was just the most bizarre and surreal accolade. I had the same reaction in Alaska, when I was filming on a glacier and a bunch of Americans started going, ‘It’s Geordie! It’s Geordie!’ Wow. I feel honoured and privileged to be part of something that is enjoyed around the world and proud to be part of such a talented team.

What’s happening for Geordie in season eight?

There’s a murder every episode and the stories are really gripping. We start with a case where a biker is found dead in a field after a charity motorbike race. Geordie and Will both realise this is a murder and not an accident. Then Will gets involved in a tragedy where somebody loses their life and Geordie desperately wants to exonerate Will. We have an episode directed by the wonderful Al Weaver, who plays Leonard, which was great. Later, Geordie gets into a tussle with Leonard over his halfway house. Leonard sees the good in everyone, but Geordie is old school and realises that not everyone can be rehabilitated. Geordie’s big story arc is that his boss, DCI Elliot Wallace [Michael D. Xavier], is trying to edge him out, and Geordie is distraught. Amongst all this, Will has a big personal crisis and Geordie goes to great lengths to help him. The last episode is beautiful and has a wonderful surprise. Also, my friend, Mark Benton, is a guest star.

How does Geordie feel about being encouraged to retire from the force?

It’s a defining moment for Geordie when he realises his shelf life has expired. He’s closed for business, he needs to move on and leave this place that he loves, and has given his life to, because he can't compete with Elliot and his entourage. Elliot’s got people in his pocket who are far more powerful than Geordie. It’s a very painful moment for Geordie and great to play as an actor. We’ll have to see if he can find a way around it.

What can you tell us about Geordie and Cathy’s story arc this season?

Geordie doesn't want to tell her he's being forced to retire, because that's embarrassing, apart from the worry of how they're going to deal with it financially. But when he discovers she's going to get promoted in her job, that makes it worse because it will affect his position in life – in the early 60s, men were the breadwinners. And suddenly, how was that going to go down with the people in the village and and at the police station when they realise that he's no longer the breadwinner and head of the household? So that's where we find those two, but we know they’ll work it out because there is genuine affection and love for one another.

You’re an executive producer and one of the lead actors. How does it feel to be the elder statesman on set?

I do feel a responsibility. I want anybody who comes on the show to feel at home. Like when we got Mark Benton, I said to him, ‘You're going to love this, Mark,’ and he went, ‘You don't need to tell me that. I've spoken to so many people who've worked on the show who’ve said it's lovely.’ When people come on the show, I want to make sure that they have fun and enjoy the process. Of course they'll work hard and know their lines and their story arc, but I also want them to have some fun. The industry can be incredibly stressful, but in the end, we're making television and that's a privileged position to be in; therefore, we should enjoy ourselves.

Tell us about casting Mark Benton in a guest role as a village copper. I'm assuming that you suggested him for the role?

I'm not sure I should be telling you this, but the part was for a woman, originally. But when we couldn't get the actresses we wanted, I said, ‘Okay, let's just imagine that the cop’s male. Do you know someone who could play a cop coming up to retirement and who was likeable and funny and could draw pathos to a situation?’ And I suggested Mark and they went for him.
He is the nicest, funniest guy you're ever likely to come across and he's an absolute joy to work with and brilliant at his craft. I've loved him for years and years.

Geordie and Will are close buddies and you’ve had Tom Brittney on your travel series, Weekend

Escapes. Can you tell us about your relationship with him offscreen?
We love each other. We stay in contact all the time. When I was in Australia filming my fishing show, he texts me, ‘How’s it going?’ and sends me a picture of himself next to Cameron Diaz – he’s working with her on a film [called Back in Action] – and all I can send him is a picture of me with a big tuna. Like James Norton, Tom is such a lovely person to be alongside – so funny, but with an intelligent wit. It's lovely to work with him. And I've never known anyone who can learn so much dialogue in one go!