"It's a bit like going into a boxing ring - there's nowhere to hide. People are prodding you, asking you for autographs, but it's part of the deal." So said Rory Bremner about celebrity fund-raisers (The Independent, 12 July) - and how partially right he was. I'd hoped that BBC's Casualty vs Bristol Medics FC (in aid of the British Heart Foundation) would be a low-key affair - 20 minutes of knockabout and a glass of pop. But as the police directed me into a packed car park next to Mangotsfield stadium, I was filled with a wondrous sense of impending humiliation. If only I'd bought some contact lenses.

I doubt anyone in Mangotsfield United plays in glasses - they'd be laughed out of the Screwfix Direct League (yes, it exists). They have stands, floodlights, advertising hoardings, a clubhouse, and proper nets that don't let the ball through. There's a sign that says "This is Mangotsfield" as you run out of the dressing room - an idea stolen by Liverpool. Today there is also a huge British Heart Foundation poster providing an ironic backdrop for a plump, immobile chain-smoker. But at least she doesn't wear glasses.

I flirted with contact lenses in my teens, and they were a great aid to disco kissing. Also, you could shake your head to the fast bit at the end of "Freebird" without maiming someone with your hornrims. But contact lenses and medical school just didn't mix. I swallowed them twice, when in a state of rough-cider-induced dehydration, and the insurance company ordered me to sift before future claims. Then there were the early-morning cardiac arrests. How can you justify five minutes to find your eyes when a brain is being starved of oxygen?

So I switched back to glasses, some nice, empathic tortoiseshell ones that make me look as if I care. Also, patients are less likely to punch you if you're wearing glasses. Now I wouldn't be without them - and at minus seven in each eye and huge astigmatism to boot, I couldn't. Not even for a charity football match. "Don't worry," said Casualty's manager. "None of our lads play, and they're in the middle of filming - so go easy." As a bit of amateur psychology, it worked - until I saw the team sheet. Where I had been expecting 11 charlies, half the team weren't luvvies at all. Jeff from Security, Eddie from Catering, Nigel the Scaffolder, "Guest Player" and "Gary's Brother."

Bristol Medics train and play regularly, at least according to the programme notes, but I hadn't kicked a football in competition for 20 years. True, I once scored a hat-trick for Preshute Panthers vs East Grafton, but 15 I realised I was allergic to those nipple-hugging acrylic shirts footballers wear. "You play a bit, do you Phil?" "A bit." "And which foot do you kick with?" "Whichever's nearest." "Great. You roam the left midfield then"

Thirty seconds of roaming, and rigor mortis set in. I switched to attack, but after 15 minutes of dismal flicks and missed headers, Casualty paid me the huge honour of not bothering to mark me. This left me free to interact with the crowd and sign autographs, or at least it would have done if anyone had had the faintest idea who I was. "Don't you get Channel 5 in Mangotsfield?" "Oi, specky. You're shit!"

But how they cheered Casualty. Every time Patrick Robinson made a save, it was if Charge Nurse Ash had saved the world. They cheered the rest of the cast, too, only I couldn't tell "Sunny Sunderland the Porter" from "Josh the Paramedic". Doctors tend not to watch Casualty - we tried it in the days of Sister Duffy and decided it was rose-tinted frippery. Even now it's toughened up, it'll never plumb the depths of cynicism and depravity of Cardiac Arrest. But then Cardiac Arrest got only a third of the viewers, and died of its own nastiness. Casualty, now into its 12th year, remains the people's choice.

And didn't the crew know it. From the dug-out with the Holby United sign to the boxes of signed photos, they knew how to stage-manage an event. Even the tradition of drawn celebrity matches was abandoned as we were trounced 5-2. "We lost our shape at the end" said Neil, our captain. I wish I'd lost mine, or at least swapped it for someone else's. 48 hours on, my left knee is twice its normal size and I can't walk. Still, in the words of the British Heart Foundation, "Thanks to Our Research, Yesterday's Victims are Today's Survivors." Let's hope so

The chant "Oi! Specky! You're shit!" has been patented by Dr Phil and must never be used again without permission.