Playwright Joe Penhall describes how he juggles the demands of Hollywood, stage and TV

From lunch with Cormac McCarthy in New Mexico to read-throughs in Kingston upon Thames...

I spent the best part of two years in America making a film adaptation of Cormac McCarthy's The Road. We shot it during a sub-zero winter in Pennsylvania, in the Rust Belt and an ashen Mount St Helens, where it was so icy and cold our trucks were sliding sideways off the tarmac. When it was cut, the director and I flew down to New Mexico to spend a day with McCarthy, showing him the film, getting his advice and having the longest lunch I've ever had. We talked about writing and what constitutes a good film idea and what makes a great book, and lastly, we talked about The Road, the movie, which he liked, saying it was "like no other film I've seen". He drove us to the airport and next day faxed through four pages of notes which were a model of frankness and precision.

I was asked to write the screenplay partly because I was the only writer out of several considered who didn't want to change anything. I felt it was important to trust McCarthy's story-telling and not be tempted to reformulate it. The producers thought this was an excellent idea and a novel approach. During filming, I spent a week rehearsing with the actors and, along with McCarthy, popped up on set from time to time. I was usually referred to as simply "the writer." The director and the actors were called by first names. People would say things like "the writer says..." or "the writer thinks..." when I was standing right next to them. I could never tell whether this was a mark of respect or whether they'd just forgotten my name. Sometimes they'd speak extra loudly or enunciate especially clearly for me, as if talking to a person who was deaf or mildly retarded. I think this is normal. In Hollywood, writers are the ghosts at the banquet. They are the poor relations of the talent. They are the only ones who truly understand the script and it freaks everyone out. But with The Road I was channelling McCarthy, with his blessing, so I was afforded unprecedented respect and cut a lot of slack.

At the moment I'm writing a film for Mike Nichols, a genius, a comedian and one of my favourite ever film directors. I've been flying back and forth to LA for meetings and writing stints. The pressure to write a screenplay as good as The Graduate is ameliorated by the fancy villa, the enormous pool, the sunshine and the great Mexican food. Two of the valets at my hotel are aspiring screenwriters and go out of their way to help me with things and daily come and find me to chat about their work. In LA most people are working on a screenplay.

I love West Hollywood: the architecture and the light and the subtropical climate, and am always struck by the generosity of Los Angelinos. I mean the real people, not movie people. Although a few weeks ago I ran into a studio boss from Warner Brothers eating sushi on the Sunset Strip and she generously said, "If there's anything I can do to help while you're here, do let me know." I said that I needed help finding a good Cookie Monster for my little boy William. The next day she dispatched her chauffeur to Toys R Us and a fine example was duly selected and FedExed to William. It's the nicest Cookie Monster I've ever seen and he adores it. I now owe her a lunch, or at the very least a muppet...

There's a lot of money and power in films. The weirdness, egomania and pressure increase in direct proportion to the money at stake. The Road cost five times as much as your average British film and was five times the hassle. After sunny LA, coming back to wintry England was like climbing in with the frozen food at Sainsbury's, but when I took my South-West train to Kingston for the first read-through of my play Dumb Show, I was oddly relieved. Listening to a cast of clever theatre actors reading and rehearsing it in a friendly, collegiate way, I felt suddenly proud. Here were people who were doing it just because they liked it. Just because they'd read the words on the page and liked them. Just because it would be fun and they would be good at it.

Dumb Show is about celebrity and confessional culture, and our endless love affair with those things which grows ever more passionate by the day. It's a reminder that celebrities and the tabloid press are in collusion, together performing a complex sleight of hand, as delicate as keyhole surgery. While I was writing it, I interviewed the notorious "fake sheikh", News of the World "investigations editor" Mazher Mahmood, about his elaborate stings involving hapless celebrities. I was struck by how much he enjoyed his work; he didn't do it for money – he did it for the love of it. He told me he got butterflies "just like an actor" before each sting and it was an incredible buzz when it came off. Inevitably he himself is a celebrity now, with his own website and book.

The odd thing about my life is that I have three full-time jobs and none of them really mix. In the theatre I'm known as a playwright. In Hollywood I'm known as a screenwriter. At the BBC I'm known as a writer of "quality TV drama". None of the people I work with know who the other people are or care. It's like bigamy. I have three jobs which I try to do all at once and it's sometimes hard to explain to people why I might be busy in LA or New Mexico or Shepherd's Bush next week, and therefore unavailable. In my house in Somerset where I write, I don't have a phone, TV or the internet. It's annoying, I admit, and it drives people crazy, but I just don't have the time.

'Dumb Show', 1 to 17 April, Rose Theatre, Kingston (0871 230 1552; Rosetheatrekingston.org)