Marc Warren plays Martin Grantham
Writer Anil Gupta explains that Martin is "a series of contradictions, not least because he himself dislikes inconsistency.
"He is neurotic yet smug, a control freak whose life is dictated to him by others notably his wife and his boss.
"He thinks he's cleverer than everyone, but can't stop telling himself so – so he's not that clever.
"A bright under-achiever, he has married above himself, but then took his wife for granted.
"He constantly tries to do the right thing – provide for his family, be there for his son, share the household chores – and is left confused and distressed when it turns out that doing all these doesn't stop things from going wrong."
"Marc Warren is a very gifted actor who has wonderful comic timing and understands that a lot of comedy is not so much about what is said but about the reaction to it.
"He has a vast range of expressions and it was a pleasure to be able to put him into situations which bring them out."
Marc is particularly well known to television audiences for his portrayal of Edward Leeford in BBC Drama Production's Oliver Twist, for Dougie Raymond in the hard-hitting cop series The Vice, as Albert Blithe in HBO's blockbuster mini-series Band Of Brothers and for the role of Danny Blue in the popular BBC series Hustle.
Marc describes his role in Mutual Friends: "Martin Grantham is a lawyer, married to Jen with a young son, Dan. He's a solicitor, a beta male who worries about everything and is slightly neurotic and anal. The glass is always half empty.
"He and Patrick are like the two sides of man – I personally would like to think that I am made up of both bits!"
He continues: "As the story opens, his best friend, Carl, commits suicide.
"One of their mutual friends is Patrick, who's a bit of a womaniser.
"The group, who were all together at university, hadn't really seen each other for a long time. The lads all went on holiday together years ago in Thailand and they are brought back together by this terrible tragedy.
"At the wake after the funeral, Martin's wife, Jen, tells him that she slept with Carl twice and Mutual Friends follows their stories as their lives begin to unravel."
Martin is hit really hard when Jen tells him about her betrayal.
Marc says : "He gets visions of them romping through the fields happy and in love, Jen and his dead best friend, and he imagines them having sex – all in his head, of course, but it affects his work and everything else.
"So when Patrick comes along, he saves the day in lots of ways."
But Martin doesn't walk out on Jen.
Marc says: "No, he loves her, he really wants to make it work and he's devastated that it's all gone wrong.
"So he agrees to go and see a relationship therapist, which are some of the funniest scenes, I think.
"They see a guy called Jolyon, who Jen's been going to visit for about nine months because she's been having therapy since she started the affair.
"And by the end of their second visit, they seem to be on the path to getting back together again."
He continues: "Jen tells Martin that she had the affair because she felt 'unfulfilled'.
"Martin is completely flummoxed when he hears that: 'What does that even mean?! You know we've been married 15 years, we have holidays, we have a nice house, had the extension done...'
"He thinks that that's all you need, but she's looking for excitement, spontaneity – she wants to wake up in the morning and not know what's going to happen, so she looks to him to change that."
Marc sees Patrick and Martin as The Odd Couple, and says: "They're both very different, but it works, the chemistry is absolutely there.
"Most of the time I'm just being very hostile to him and he just takes it and it's hilarious!"
As for comparison with Sideways, Marc says: "I'm trying to work out which one I am – the bald one, Paul Giamatti, and Xander's the blonde one. Which means I'm the one who knows about wine! Yep, I like the idea of that!"
Marc would love to see Mutual Friends turn into a long-running series.
He says: "I was working in Los Angeles when they sent me the original script for the pilot episode, which I loved, and they flew me back for a week's rehearsal and then we shot it, so it was a very quick turnaround.
"I could see Xander playing opposite me straight away and I just thought it was very funny."
Marc's trip to LA was a success; he was cast in the feature film Wanted with Morgan Freeman, Angelina Jolie and James McIlroy.
He says: "I played one of Morgan Freeman's assassins. I've always wanted to do a big Hollywood film – although this one was filmed in Prague, so I really kind of kept my eye on the prize and was very focused in what I wanted and I was fortunate enough for it to happen."
Marc actually turned 40 while he was out in LA.
He says: "I drove up into the desert and spent three days in Vegas celebrating.
"I went to see the Cirque du Soleil in the evening and when it finished at midnight I was 40.
"I'd always wanted to do that five-hour drive from LA to Vegas. I set off at four in the morning and watched the sunrise – just me.”