Cold Call: Jack O'Sullivan rings Will Macdonald

TUNE INTO Channel 4's cult show TFI Friday, and you will be bemused by the weird relationship that the brash Chris Evans has with his producer, Will Macdonald. This boyish, bashful Old Etonian is fast becoming a celebrity in his own right. But he plays stooge to Evans, submitting to ritual humiliation, be it dressing up for Evans in micro leather hot pants with red stilettos, allowing himself to be given a painful electric shock, or letting Evans slag off his ex-girlfriend in public.

Will likes us to think he is a cheerful chap, always up for high jinks. His new book, How to Be a Pub Genius, offers 50 tricks "guaranteed to wow babes and win beer". I am ringing him because I am worried. He doesn't seem very happy to me.

We start with his cleverest pub trick. "The best ones," he says, "are those that obey the basic laws of physics. For instance, did you know that if you fill a glass of water to the brim, you can still fit 50 five- pence pieces in it without spilling any water? It is all thanks to our old friend, the meniscus."

"The meniscus?"

"The circular edge of water held together by surface tension." Of course, I say, remembering that Will, for all his antics, is in fact a scientist with a zoology degree from Oxford University.

"You are really a pretty serious person, aren't you, Will?"

"You mean I'm not very funny?"

"No, it's just that you don't seem proud of being serious, and you cover it up with a smokescreen of silliness."

"I just don't want to disappear up my own arse."

"But it is more than that," I reply. "It is that whole English elite thing of working terribly hard to make life look effortless."

"No," he says. "I am reacting against being taught always to take myself seriously. I wanted to lighten up. I am saying that it is funny to be hit in the face by a five-pound herring and fall over.

"Otherwise, you can just disappear into your own gloom."

"Are you gloomy?

"No, not at all, but I have got elements of that," he says. "I am quite introverted compared with Chris. He says what he thinks, whereas I don't say things out loud. It is part of being southern. I wish I could let more out. Earlier on this year, I got a cyst on my vocal chords, which was put down to me not screaming out loudly."

"Will," I say, "why don't you stop trying so hard at being lightened up? You're all right. It's OK to be a serious person."

"But I don't feel I'm trying hard," he replies. "I couldn't have tried less hard writing this book. Everyone should be allowed to do what they want instead of people picking holes in it and telling them why they shouldn't do things. I agree I used to try too much but not anymore. I always tried to keep everybody happy, rather than telling people straight and pissing people off."

"So have you managed to lighten up enough yet?"

"I think I could lighten up a bit more. The main thing is to be happy. People get exasperated with overt seriousness."

"Will," I say, "I can't work out whether you are getting there or singing in the dark?"

"I think I am getting there," he says, "But are you?"

We've reached an impasse, so I ask a final question. As a zoologist, which animal would he like to be?

"A male blackbird. He sings first thing in the morning. But it's a stupid time to sing because he is hungry. It's a show of strength. The ones who can sing the longest are obviously the fittest and the ones the females want.

"Make sense of that."