The vet bill has been sitting on my desk for three weeks. All vet bills are cruel and unusual but this one is even more so than most. It only came about because the owner of the yard where I had the horses until recently kept telling me they were lame. They didn’t look lame to me.

‘Maybe she’s just tweaked herself in the field?’ I said, as we trotted Grace the skewbald pony up and down.

‘She’s lame as ****!’ he declared, in his charming horseman’s patois. The thoroughbred filly, meanwhile, he declared utterly beyond help.

‘She’s club-footed,’ he growled.

‘Well, maybe one front hoof’s a bit taller than the other,’ I said, bristling like a mother who has been told her daughter needs an orthopaedic shoe.

He shook his head. ‘Her feet are completely odd. She’s gonna blow a tendon.’

Horsey people are like this. They either let everything go merrily to pot, or they fret about every last limp quite as if they had Munchausen syndrome by proxy.

The warning signs were there that this one was a fretter after I asked him for advice about the Volvo overheating one hot day. ‘You need to get rid of that car quick,’ he said, a wild look in his eyes. ‘The head gasket’s about to blow.’

After Googling, I discovered that because I had put the air con on full blast in heavy traffic, the old diesel engine had drained the fluid. I topped it back up, wound down the windows, used neutral while queuing and it was fine. But try as I might, I couldn’t persuade the harbinger of doom that my horses weren’t about to blow a gasket.

In the end, it became a moot point as I decided to move the horses back to Cobham anyway. But not before he demanded I have the vet out.

My jovial James Herriot came and watched them trot up and down before declaring them both healthy and sound, while chuckling effusively at the irony of the pointless callout. Darcy was a bit footsore from the hard ground so he left me a box of phenylbutazone.

The bill arrived the next morning. In what other industry do you receive a paper invoice on your doormat a few hours after the work has been done? After seeing them at lunchtime, the vet must have put the paperwork through on his iPhone while sitting in the car park, and had the girls in the office catch the last post, special delivery, to get the bill to me the next day.

‘That can mature,’ I thought, putting it on my desk and estimating, based on previous experience, that a callout to two horses who turned out to have nothing wrong, plus a small box of Bute, could come to anything between £80 and £380. I really ought to find out, but I couldn’t face opening the envelope.

It was still sitting there on my desk three weeks later when Gracie, now at her new home in Cobham, started looking colicky.

I had ridden her out and she had been very sluggish. When we got back, she put her tail in the air and began to — I can’t put it any more delicately than this — strain.

‘Oh, for the love of all that is holy!’ I told her. ‘I haven’t paid the last vet bill, you can’t have colic yet!’

Gracie lifted her tail again and made a quite pathetic attempt to force out a poo. But poo came there none.

For those who are not horsey, I must explain that constipation in horses is not just inconvenient or mildly amusing for the purposes of a column. It’s life-threatening. If the gut stops, it’s a flushing procedure at both ends, and if that doesn’t work, hospitalisation and major surgery. Eh voilà — your stuck poo has come to £5,000.

There was only one thing for it. I led her back out towards the school. Then I realised I would need a whip. ‘Can you hand me that crop?’ I called to the yard manager, who was filling haynets.

‘Oh dear. Are you going to beat it out of her?’ she said, aghast.

I wouldn’t put it quite that way. But the only way I know of getting a horse’s gut moving is to move the horse.

As soon as the crop passed into my hands Gracie perked up and span round the school at the rate of knots. After a couple of circuits she stopped, made the straining face, and out shot a steaming triumph.

‘Bingo!’ I shouted. Then, after she did another one: ‘Hallelujah! Oh, thank you, God!’

The yard manager looked at me like I was mad. I’m not mad. I just don’t want another vet bill until I’ve paid the last one.