Dom Joly: Only in France do they run marathons fuelled by wine

Last week I was filming in and around a lovely, hot Bordeaux. On my second day there, after a strenuous day at "wine school" (who knew such a wonderful institution existed?), I came across the Marathon Du Medoc.

Why have I never heard of this event before? I normally loathe marathons with their "look at me, I'm doing stuff for charideeee" overload, coupled with that organised "we're having fun" spirit that never fails to annoy. This event however, has a cunning twist. Runners are steered through some of the top chateaux in Bordeaux where they are not offered water or high-energy drinks at the roadside – they are offered wine.

Every chateau that the runner passed by had set up tables outside with jeroboams of seriously decent wine stacked up in cases behind them. Eager volunteers, themselves fuelled by the fine wine, held out paper cups of the best vintages for the runners to grab and gulp as they tramped past. It was hilarious.

We were invited into many of the chateaux to film the event ... and sample the occasional glass or 10. At the first stop everybody was laying into the wine and dancing to a band that had set up in the ancient courtyard. It all looked like great fun except for the pervading stench of sweat and having to put up with Frenchmen murdering Rolling Stones numbers.

For some reason there were a lot of Japanese lady runners and there seemed to have been some cheeky mix-up in the translation of the dress code. Whereas everyone else seemed to be dressed as animals, they had come as sexy French maids. This being France, nobody was complaining, and everyone seemed incredibly keen to ply them with wine.

We drove on to our next filming spot about 16km into the race. To get there we cut straight across the countryside as the marathon did a big loop. Rather wonderfully we were not alone in spotting this route: about 20 or so runners – two of them on mopeds – had also decided to take a little short cut. They sat beside the road drinking until the pack arrived and then rejoined the "race". It was all very French.

The pack had lost the early enthusiasm of the first stop. They were still slogging on and still accepting free glasses of wine but it was clearly taking its toll. The owner of the chateau here told me in great seriousness that red wine was fabulous for runners as it contained sugar. As we talked a man dressed as what was probably once a chicken tried to grab a glass of wine, missed and staggered into the table knocking about 10 jeroboams over. "Not to worry," said the chateau owner. "That was the 2008 – not my favourite ..."

At about 22km in we sat on a particularly beautiful terrace overlooking fields of vines that stretched all the way down to the Gironde. The golden sun blazed down on the surreal scene below us; a human stream of people dressed as cows, seagulls, ladybirds, doggedly jogging along between the vines, many of them three, even four sheets to the wind.

As I watched, one man from a rival chateau peed contentedly all over his rival's grapes. Meanwhile, a man dressed as Jesus, complete with a large wooden cross on his back, chased a man wearing an 8ft giraffe costume until Jesus tripped up and went head over cross into the vines.

I think he'd had a touch too much to drink. I waited for a minute or so but he didn't rise again. If I ever run a marathon (which is extremely unlikely) then this will most definitely be my first choice.