Still snickering as she staggers to her feet, Tui swipes the boot from my hands and starts to put it on sans sock, tumbling into me on her unsteady foot.

‘Oh no,’ I tell Beavis, ‘Tui is drunk again.’

Such is Tui’s mirth that she is still laughing when we emerge from Keith’s stable ten minutes later, and I’m forced to make her count calmly to twenty before helping her to mount. Watching how much she is coming on continues to be the unrivalled highlight of my time here in New Zealand. She has spent hours up in the saddle while I instruct from the ground, taking her right back to basics and starting with her seat and leg position, before progressing to sitting trot, rising trot, and finally, a week or so ago, tentative cantering. Keith seems to know that he has a very precious cargo up on his back and behaves accordingly, barely flicking an ear when Tui gets carried away and starts flapping her arms, or her legs, or both consecutively. Today, we are going to tackle jumps again, and this time I want her to ride over them without being led by me – a big step.

‘Very good, Tu!’ I praise, as she pops over a tiny cross bar. ‘But next time, remember to bend over forwards from your middle, as if you’re bowing to the queen.’

‘Okaaay.’

‘And bring your hands up along Keith’s mane, as if you’re going to tickle his ears.’

‘OK, Gee-nie.’

After she has successfully cleared a row of small jumps, I prop the poles up a fraction higher, flicking the lunge whip through the air to encourage Keith forwards. There is a dicey moment when Tui loses a stirrup after the first fence, but she manages not to fall, and even slots her foot back into place without any assistance from me.

‘You’re doing so well,’ I tell her. ‘You’ll be winning the Grand National in no time.’

‘What?’ she bellows, looking down at the pony’s outside foreleg to make sure she’s rising to the trot at the right time.

I am just about to explain what the Grand National is when Tui interrupts me with an excited shriek – one that is loud enough to send an alarmed Keith veering off course and cantering skittishly towards the gate. Assuming that he will stop when he reaches it, I don’t bother to give chase, but the next second the determined pony has taken an almighty gazelle-style hop into the air and cleared it by inches. Tui, to my total astonishment, not only manages to stay in the saddle, but remembers to fold forwards, too.

‘Bloody hell!’ I shout, throwing down my whip and hurling myself across the muddy ground. If Keith has decided to bolt, he could be halfway across the yard by now. What will Bonnie say if Tui goes missing again – and on my watch?