And, while a lowly C1 may not be the most prestigious or fastest competition car ever built, proof that it’s the racing, not the machine that counts is what attracts everyone from gangs of mates on a shoestring to experienced, affluent drivers moonlighting from GT3 and top-flight historic series. All this becomes clear as I start my first stint as one of four drivers in the C1 Racing Club’s own car. I’ve done about three laps in daylight but, by the time I strap in, Spa is brooding under a silvery, moonlit sky.

As I merge onto the Kemmel Straight I’m down by about 20mph on the pack of cars who’ve carried their speed through Eau Rouge. And I’m basically trying to keep out of their way until I can pick up momentum on the downhill return. It’s chaos, C1s circulating in packs, locked in private battles, while mad bike-engined, Citroën-based prototypes scythe their way through and everyone dodging the slow-moving regular 2CVs, trundling along gamely at half the pace of everyone else.

It’s not unusual to have a pack of a dozen cars of wildly different speeds all converging on one corner, lights dazzling you in the mirrors as you try and second guess whether you’re overtaking or being overtaken. Somehow it works and you get a few seconds to catch breath before you have to do it all again. And, modest power or not, by the time you reach the fearsome downhill left-hander at Pouhon you’ll be doing 90mph-plus and sliding sideways as the budget Nankang tyres start to let go.

Lap after lap, hour after hour these battles go on, slipstreaming up Kemmel and then ‘doing a Hakkinen’ on some unsuspecting 2CV – a winning technique for gaining a place into the Les Combes chicane. And then it rains. As it always does at Spa’s most exciting races. One thing watching it from the sofa on a Sunday afternoon. Another entirely at 2am when the spray is so bad you can’t see the track surface, your tyres are shot and there are people ricocheting off the barriers in all directions.

With nearly 70 C1s on track – two thirds of those from British entrants – and lap times separated by just a few seconds you’re never far from a battle. In my second stint I enjoy one that goes on for maybe 10 laps, my rival and I fighting fiercely for every corner but able to exchange a friendly thumbs-up at the shared thrill as we swap places on the straights. And that’s what it’s all about. No quarter given on the circuit and relaxed, ego-free camaraderie in the pits. In a car you could build and enter from scratch for less than £5,000. Pure racing, the like of which attracts high-rolling racers to gangs of mates alike. And levels the playing field in a way few other series have achieved, for a price within reach of nearly anyone. That’s why you’d want to race a C1 round Spa.