You’re also filming Gulliver’s Travels?

I am – I’m leaving in two weeks for England and I’ll be there for five months. I’m a huge fan of England.

As strange as it sounds, when I’m writing something I like to go to a city that embodies the spirit of what I’m writing.

So I wrote Forgetting Sarah Marshall in Hawaii and there’s something about London that makes me think of the Muppets.

I was surprised that people call each other muppets, like a vague insult!

Are you going to be in Forgetting Sarah Marshall spin off Get Him To The Greek?

No – I’m writing a lot of the music for it though. I’m writing Russell Brand’s music and there’s a female character that’s kind of like Fergie and I’m writing the music for her as well.

What do you think of Russell Brand?

He was my entire inspiration for my character in I Love You, Man. I was so jealous of Russell for how much he ‘popped’ in Forgetting Sarah Marshall that I thought it was an opportunity to do my American version of him.

So I put on a swagger and just tried to be really cavalier. Russell has this attitude that I don’t have. He’s like: “This is who I am, take it or leave it”.

He’s very comfortable in his own skin and I’m very awkward in mine, being that I was 6ft 4in from the age of 12.

Now things are going so well in your film career, are you going to duck out of your part in TV show, How I Met Your Mother?

Actually, just the opposite. I just signed a one-year contract extension. I’ll be there for four more years. I feel very lucky to be on that show. They came along at a time when I was totally out of work, so I can never feel anything but grateful.