Rose Byrne: “Dan was really great with on-set improvisation, very accommodating. With all the comedy I have done so far, the laugh wins: so whatever’s funny wins. We would always be pitching ideas and lines and thoughts, and it was really good to do some physical comedy as well with the running and bits and pieces. So I would say it’s like eighty per cent scripted, twenty per cent improv.”

Rafe Spall: “Yeah most of the really funny bits were improvised…”

Dan Mazer: “Well, Rafe would come in on his days off and just, y’know, improvise on behalf of other people, just to spruce it up…”

Rafe Spall: “I’d do a bit of work, come in, do a bit of work with the actors, give it a bit of a polish, give it a bit of a buff…”

Dan Mazer: “What was brilliant and what I did very deliberately in the casting process, and one of the reasons I loved Rafe initially, is that I wanted to cast people who were brilliantly funny in their own right. People who you could sit down in a room with, and know you could have a laugh and that their first point of call was comedy, and that they would be comfortable and easy with comedy.

“Because I want this film to be first and foremost funny, so it would have been ridiculous not to let people improvise, and so when you’ve got people like Rafe, Rose, Stephen [Merchant], Olivia [Colman], and everybody, all those people who are naturally funny on set, you’ve kind of got to let them do their thing.

“It’s like Lionel Messi on the pitch and putting him in goal, it would be an idiotic thing to do. So they all went out there and they were brilliant. “

Rafe Spall: “Yeah and that’s a really nice thing to have someone, who is encouraging you to do that, but most of it was rubbish. It’s true! The nature of improvising is quite vulnerable in a way, because you have to throw so much stuff out there, it’s like you throw everything against a wall and see what sticks, because you’re all just searching for inspiration really, and every now and again you’ll get a gem, and most of the stuff…”

Dan Mazer: “No, I think most of it was brilliant. I ended up with a three-hour assembly of this movie and, when I came to edit it. Some of the funniest stuff in the movie comes straight from the actors, and it’s brilliant to have that resource, and for me to get the credit for it. So, if we could actually cut out all the stuff that was improvised and say it wasn’t, that would be ideal.”