Image copyright Helen Maybanks Image caption Stephen Merchant is making his stage debut in The Mentalists

"Two years ago I wouldn't have imagined doing this," says Stephen Merchant after making his stage acting debut this week in The Mentalists in London's West End.

Merchant stars opposite Steffan Rhodri in Richard Bean's darkly comic two-hander as angry, frustrated middle-manager Ted, who wants to create his own utopian society.

Bean, writer of hit farce One Man, Two Guvnors, has even tweaked his 2002 play to make reference to Merchant's West Country accent.

Best known for co-writing and directing TV series The Office with Ricky Gervais, Merchant's other TV work includes Life's Too Short and An Idiot Abroad. He appeared in the comedy films I Give It A Year and Hall Pass, while his stand-up comedy show Hello Ladies went on to become a television series for HBO.

In this interview, he talks about Ricky Gervais, living in LA and his latest foray in Hollywood.

Image copyright Helen Maybanks Image caption The Mentalists is at Wyndham's Theatre until 26 September

How different is stage acting to doing stand-up?

One of the things I discovered early on was that I had to switch off my "stand-up" brain. With this play, I had to zone out the audience. It took a week to get used to that.

It's a dark and unusual play, you can't just be chasing laughs. That was one of the reasons I wanted to do it.

I've most enjoyed immersing myself in the character and thinking about back stories, improvising and getting photographs of people we refer to. It's proper acting!

It's a Richard Bean play so it's very funny, but it's also very dark. How have people reacted?

People have come and told me that they were really moved by it. I think people who expect a One Man, Two Guvnors will be surprised.

It's quite an adult piece. That's what attracted me - two dark souls who are lost, overgrown men with this weird bond. I think it's quite touching.

Image copyright Helen Maybanks Image caption Stephen Merchant and Steffan Rhodri play oddball friends holed up in a hotel room

Could this lead to other stage roles?

I was always intimidated by the thought of learning the lines, but now I've done it I've really enjoyed the process.

I've been tantalised by staying in character, it's unlike TV and film where it's a very bitty process. I think my experience of this is going to feed back into my writing.

But at the moment I'm so tired. It's exhausting. It's basically people on stage shouting. So I won't be able to tell you that until I've finished the run.

Don't expect my Macbeth anytime soon.

Lear, maybe?

Lear with a West Country accent!

Have you thought about writing for the stage?

That's intrigued me - the idea that you are working with a live audience, which is something I always liked about stand-up.

I like writing with certain parameters, like we had the documentary [format] in The Office. I have my days free now so maybe something will percolate.

Is Ricky Gervais coming to see the play?

I don't know where he is in the world. He's an international jet-setter now.

I don't think Ricky has ever come to a gig. He doesn't like leaving his house after 19:00.

I used to invite him to birthday parties and he'd say, 'That ain't going to happen - I'm not going to come to a birthday party and listen to pop music.'

Image copyright Helen Maybanks Image caption Morrie (Steffan Rhodri) films Ted (Stephen Merchant) as he outlines his utopian vision

How do you find living in Los Angeles?

I've come back to London in the heatwave so that's helped ease me back in.

It's nice to be back with British people who understand me and the way I think. It's useful to have that healthy dose of British cynicism, because you can live in la-la land and lose touch with all that.

I've also liked immersing myself in the theatre world. I'm going to be wearing a cravat next time you see me, swirling in and out of the Groucho [Club] saying, 'Hi love.'

Before the play you shot a film called Table 19 - what's that about?

We shot it in Atlanta. It's a comedy drama with Anna Kendrick and Lisa Kudrow in the cast. It's about a bunch of oddballs and losers thrown together on the worst table at a wedding.

It was a thrill for me. I got to work with Craig Robinson who used to be in the American version of The Office. And Tony Revolori who was in The Grand Budapest Hotel. We all became very good friends. I had great pleasure just making Lisa laugh. I found I could tickle her funny bone.

My character is a sort of slightly odd, socially awkward ex-convict - not a tough, hardboiled one, but a white-collar convict.

When we weren't filming I was learning the lines for this play, so it was useful having time stuck in a trailer.

The Mentalists is at Wyndham's Theatre until 26 September.