I was nervous about playing a lead part in a Working Title romantic comedy and I was also nervous about the fact that I not only had to take my clothes off, but get my willy out. There's certain things you can do to make yourself look better, but there's nothing you can do about your willy. Your willy is your willy and no amount of working out is going to make your willy look any different. You get what you're given. But I wanted to look my best and to whip myself into any semblance of handsomeness. And that was hard going.

You do stuff that gets a reaction and you think 'that's a winner' and then it never sees the light of day. But the thing with improvisation is that 90% of what you come up with won't be used and for good reason. But you keep going for the occasional gem that you might come up with. You do a scene and a lot of the time. We wouldn't cut. So, you come up with something that might be funny and then you go, 'alright, what else'? So, you kind of throw stuff against the wall and see what happens. But you've got to be prepared to make a fool of yourself.

If you're a casting director, you're going to be curious to see what Timothy Spall's son is like. But when you get in the door, you have to have something to offer.

I watched what I ate for a bit and did a bit of exercise. I wanted to look alright because I knew I had to take my clothes off and I knew I was starring alongside some extremely attractive women! I think it was Humphrey Bogart who said that the only reason people found him attractive was because of the attractive women he played opposite. So, as audience member you go: "Well, if she would find him attractive, then surely I must too!" Playing opposite beautiful actress of the calibre of Rose Byrne and Anna Faris is amazing - it does a lot of the work for you.

I was nervous about playing a lead part in a Working Title romantic comedy and I was also nervous about the fact that I not only had to take my clothes off, but get my willy out. There's certain things you can do to make yourself look better, but there's nothing you can do about your willy. Your willy is your willy and no amount of working out is going to make your willy look any different. You get what you're given. But I wanted to look my best and to whip myself into any semblance of handsomeness. And that was hard going.

I've done loads of things people have never seen, dramas on BBC4 and plays upstairs at the Royal Court and the Bush, and because I didn't go to drama school, they gave me an education.

I'll probably always be 'Timothy Spall's son' and it's something I'm proud of. Maybe one day as well as that, they'll say of Timothy Spall that 'He's Rafe Spall's dad'.