Because I’m reckless, stupid and irresponsible, I normally get landed with the biggest, most obstreperous hunters. But the other weekend the riding school boss, Jane, decided to allocate me a different horse to ride. It was a smallish grey called Potato.

‘What’s he like?’ I asked one of the regulars. ‘Oh he’s lovely!’ she said. But I didn’t necessarily believe her. One of the things I’m learning about riders is that they lie through their teeth about how nice particular horses are. Something to do with the convention that misbehaviour is always the fault of the rider, never the horse.

‘He’s not very big,’ I complained. ‘How does he jump?’ ‘He doesn’t,’ my friend explained. ‘He’s a polo pony.’ Now I was starting to get quite sulky. I’m not saying I’m obsessed with jumping or that it doesn’t make me afraid. But I do know I need to do a lot more of it if I’m to be ready for next season and get my book Mister Delingpole’s Sporting Tour underway.

So I got onto Potato. I hardly needed the mounting block. And I looked at the riders who’d bagged one of the hunters, towering above me, thinking how unfair it was that they could have a go at the post and rails and I couldn’t.

I steered Potato towards the water trough to give him a drink. Every time I do this, I find myself thinking of the old adage, because it’s so true: you really can’t make a horse drink if he doesn’t want to. Potato did, though. He drank with ponyish enthusiasm and I began to warm to him.

Not as much as I did once I’d ridden him into the first field. ‘Woah!’ I declared to anyone who’d listen. ‘This pony is totally awesome!’ And he was too. Riding a hunter — a big, sturdy horse bred to jump over huge hedges and keep going all day — is like driving a Range Rover: big engine, lots of power, but a bit crap if you’re trying to nip in and out of tiny parking spaces. A polo pony, on the other hand, is more like a hot hatchback, such as that ludicrously inappropriate Golf Four Motion I acquired for next to nothing the other week. Instead of taking ages to get going, as my regular mounts Ted or Freddy do, this little number was nimble and responsive: just a slight squeeze and — vroom! — off he’d shoot. And the cornering! Wow! ‘I’ll tell you how to turn a polo pony,’ barked Jane. ‘How? How?’ I asked excitedly. ‘Shorten your reins a bit, put them in one hand and just turn your body.’ So I did. Wow and double wow! ‘These things can turn on a pin!’ I said.

And so sensitive. One of the maddening things about learning to ride is the myriad hours of frustration you have to put in kicking and squeezing reluctant nags to no avail. But a polo pony is a flattering beast. He makes you feel like one of those riders you see on TV, in control and in command, so that when you launch your lightning escape from Lord Baelish’s henchmen you just know they’re never going to catch up with you. ‘I expect Bucephalus was just like Potato,’ I mused.

Afterwards, Girl reported back to her mother. Apparently, I had behaved quite appallingly. ‘Dad was the most embarrassing thing ever!’ Girl said. ‘He was going round and round in circles saying: “Look at me, every-one! I’m practising my polo turns!”’ I’m afraid she wasn’t exaggerating. And the next day was even worse.

So determined was I to extract full value from my hour’s ride on Potato (£20! What a bargain! Is there any other pursuit where you can have that much fun for 20 quid?) that I began breaking all the school’s unspoken rules. Rule number one is that you only do stuff like cantering or jumping when Jane says you can. But I’m afraid I was naughty. At the end — desperate for a last canter, which is so different from a hunter’s canter, less like settling woozily into a comfy chair in a gentleman’s club after a magnum of claret, more like trying to outrun the Zulus at Fugitive’s Drift — I pretended I’d sort of lost control and let Potato hurtle at breakneck speed towards the gate, reining him in just in time to stop him crashing into the flank of one of the little ones on a pony.

There was much tut-tutting from the grown-ups. ‘Well that does at least explain why we had a rider fly over his head last week,’ Jane observed drily. ‘He does come to quite a sudden halt.’

Why am I telling you this? Well, it’s partly to keep you up to speed with my on-going midlife crisis, partly to urge those of you who haven’t had the pleasure of riding a polo pony urgently to consider doing so before you pop your clogs. And partly so I can dwell in melancholy fashion on what a bloody tragedy life is for those of us whose natural mental age is round about 14.

Yes, I know we all feel younger than we are. But some people are very comfortably middle-aged even in their early twenties and unfortunately for me, I’m not one of them. As I (very) fast approach 50 I’ve acquired many of the attributes, it’s true: receding hair, an increased fondness for tweed and Viyella shirts, a burning hatred for almost anything that happened after about 2007. That’s all just surface, though. Proffer me a bag of MDMA, give me the keys to a rorty Golf, put me on a pony that makes me feel like Alexander the Great and that’s it, I’m gone, mate. Forever young; forever doomed.