Hugh Bonneville, 50

A TV and film actor, Bonneville (left in picture) is best known for playing the patriarch Earl of Grantham in ‘Downton Abbey’, and boss Ian Fletcher in BBC docu-spoof ‘Twenty Twelve’ and follow-up ‘W1A’. His films have included ‘Notting Hill’ and ‘The Monuments Men’. He lives in West Sussex with his wife and son

About five years ago I presented a prize at the Crime Thriller Awards and unbeknown to me, Peter passed me on the podium to pick up the People’s Bestseller Dagger award. It wasn’t until a year later that we properly met: a producer wanted me to play Peter’s iconic character, Detective Superintendent Grace, in a TV adaptation. So we met at the East Beach Café in Littlehampton, West Sussex.

I was expecting a mysterious-looking man with a dark fedora and shifty eyes. Instead I met this fit-looking, urbane, deeply inquisitive person. During the course of lunch it became apparent to me that I wasn’t quite right for the role – but the upside was that we hit it off.

We had a memorable afternoon the first time he invited me and my family over to his house: we played in his swimming pool and afterwards, ended up playing a game with his friend [the horror author] James Herbert: each of us took it in turns to wear these silly paper masks and had to guess which face we were wearing; I was [the comedian] Peter Kay, which took me three hours to work out.

I find his work routine fascinating: his best hours are 6pm to 10pm. He makes a gin and tonic, lights up a cigar and cracks on. I rather admire that he doesn’t dread what he’s got to write; he celebrates it.

I’ve read his books with great pleasure and I’ve realised what a huge international name he is in that genre – and how lightly he wears that fame. I think what sets him apart is how he writes with such authenticity and accuracy: he spends more time in the back of Brighton police cars than a regular felon. And he’s told me about all these officers that he’s become acquainted with.

Peter has a dash of James Bond derring-do that I lack. He’s fit as a fiddle and loves his classic cars; I’ve always pootled along fine with a Mini Metro. I think I lack his panache.

Even though he travels an extraordinary amount, giving talks and promoting books, we’ve kept in touch. He’s diligent with his fans despite some of their interesting claims; one kept telling him he was the reincarnation of the maharaja of Jaipur. But he treats them all with great respect, which is really endearing; he has more patience than me.

He’s given my 12-year-old son Felix some great advice on thriller-writing. Felix loves writing stories and has sent him some of his work; Peter didn’t talk down to him, but rather commented favourably on certain elements and pointed out areas that could improve.

He’s a great follower of Downton Abbey, so we talk a lot about his interest in my world; how I’m at the mercy of 120 other people on a set. I wonder whether, if I sat down to write, I could cope with the solitude.

Peter James, 66

A former film financier, James has since written 26 novels and is best known for his bestselling crime series starring Detective Superintendent Roy Grace. He divides his time between Brighton and west London

I was in Thailand with a blinding hangover when I checked my Twitter account and saw that Hugh had said he was reading my book Dead Simple and loving it, which cured my hangover. We chatted on Twitter for several days, talking about bits of the book he liked.

We began emailing and met up for lunch at the Ivy, in 2008. Before becoming an author I’d worked as a film and TV producer, and almost all actors tend to be shorter than you’d imagine – except with Hugh, who was much taller than I expected, with terrific posture.

I knew he’d played a cop before, in a BBC series eight to nine years ago, and I thought him convincing; sort of Morse-like – tough but warm, qualities I really liked. So we talked about that, and him playing Roy Grace. There was an instant click and though the adaptation didn’t move forward, we became friends.

He’s quite a dapper dresser. Last time I had lunch with him, he turned up in a smart three-piece suit with a waistcoat, which is unusual these days; a lot of actors dress down. But he looks elegant in nice clothes so he dresses up even in his house, or when he’s coming to see us in Brighton. I can’t remember if he dressed that way before Downton, though!

For me it’s been a lot of fun talking about the behind-the-scenes world at Downton with him: though they all seem to get on pretty well, they change the directors every two episodes, which might help keep it fresh. I know Hugh is booked up two years ahead with it, but it can’t go on for ever; part of its problem is how many more years it can jump. I’m hopeful that Hugh and I can do something together one day: there’s a genetic scientist in one of my books who I think he would be perfect to play.

Because writing is sedentary, my way of relaxing is thrill-seeking: I race classic cars. But being in the limelight means Hugh’s working life is fairly full-on, so his idea of chilling is to retreat into his beautiful house in the depths of the Sussex-Hampshire border.

My writing success didn’t happen until my mid-forties, but if it had happened at 21, I might have been an arrogant celebrity. And maybe it’s been the same for Hugh. In the past, I’ve worked with a lot of stars: you go to a restaurant and they’ll always ask for something that’s not on the menu, because they can. What I love about Hugh is how he’s successful, but retained his humility.

The 10th Roy Grace novel, ‘Want You Dead’ (£7.99, Pan), is published in paperback on Thursday. ‘A Twist of the Knife’, James’s debut short-story collection, is published in hardback (£18.99, Pan Macmillan) on 6 November