"WHO'S the other guest?"

"Patrick Moore."

"Well, they won't touch him. He's a national treasure. So what have they got on you?"

"I've no idea."

"You must be fucking mad."

So pronounced a colleague after I'd agreed to appear on Have I Got News For You. I wasn't going to until Boris Johnson kindly bleated in The Spectator that it was a pre-scripted fix. If I could just get my hands on the script, cover all the angles and come out fighting. So, I agreed, on condition that they bike a copy down for me to digest in advance. I waited in all day Monday. Nothing. And Tuesday. Nothing again. Bastards.

When I arrived at the studios, I was spat at and jostled by the security staff. One knocked off my glasses and crushed them under an orthopaedic shoe. Then Ian Hislop appeared through a cloud of dry ice in a pink crutchless tutu screaming: "Hey, ginge! We're going to dance on your grave tonight." Or it could have been: "Hello Phil, would you like a cup of tea?" On the way to make up, I passed Paul Merton dressed as some sort of reaper. He looks so nice on TV, but when I asked to see a copy of the script, he brought his scythe down on my left arm and sliced it clean off at the elbow.

Fortunately, this left me one for the tea which, in all fairness, was thoroughly pleasant. Unfortunately, it had been spiked with the date-rape drug rohypnol. The rest of the evening is a blur. I have vague memories of the dark, shadowy images of Hislop and Merton bearing down on me from either end, while Deayton smirked and a large man with a monocle used my mid-section as a xylophone. I was discovered three weeks later in the staff toilet at Limpley Stoke Happy Eater. A tough gig, but a picnic compared with Tibs and Fibs.

Tibs and Fibs - you may remember - was a madcap medical quiz that faded out of the Channel 5 line-up a few months ago. The 26 episodes took 10 days to record, and most nights we were turning round three shows in a session. The studio audiences ranged from seven to 70 - in age and size - and there were some decidedly dodgy rounds (eg: Dr Hilary asking Craig Charles to draw the symphisis pubis on a bikini-clad model with an indelible pen).

But it was the structure that really did for it. The captains were both doctors and we knew most of the answers. The guests weren't and didn't. So either the guests had to be pre-briefed with the correct answers ("Craig, what are mittelschmerz?" "Ooh... I know. Is it pain in the lower abdomen experienced about midway between successive menstrual periods"). Or the questions had to be dumbed down ("Who knows a song with doctor in the title?") or the scoring had to be totally abandoned.

We went mainly for the latter - a big mistake because no matter how stupid the show, the audience care about the score. And so should the contestants.

Ian Hislop warned me at the outset of HIGNFY that we would lose. "Paul is doubly competitive. He'll start by being funniest and then when the `odd one out' round comes in, he starts concentrating on winning. But at least it gives other people the chance to crack a joke."

In fact, the skill of the show is that Deayton allows contestants the space to spar whenever they want to. With only one show to record, there's all the time in the world to shine or make a complete tit of yourself. The result lasts 75 minutes but edits to 30 - not just to cut out the dead wood but to balance the contributions and damp down slander and obscenity.

As for preparation. Deayton links from an autocue. Wow. There is no script or rehearsal. You do get to see - very briefly - the video clips, odd one out and headlines two hours before kick off. This is primarily to stop new guests soiling their pants. But all it really does is provide a structure to ad lib around.

Once the rohypnol kicked in, my contributions became ever more unpredictable, but each time Merton trumped them with something much funnier and with impeccable timing. I had captained 26 episodes of Tibs and Fibs without smiling once, and within a minute I was grinning like a village idiot. Deayton and Hislop, too, are happy living off their cuffs. Take it from a doctor. These boys can improvise.