‘Start at the back and try to pass as many horses as you can,’ said the trainer, as we stepped on to the all-weather track at Lingfield.

It was only a practice gallop but I couldn’t have been more excited if I’d been lining up for the Gold Cup.

Darcy had been loaded on to the lorry that morning with eight other horses for an outing to see if any of them happened to show signs of what the trainer calls blistering speed.

Unless your horse has blistering speed you can forget going ‘under rules’. When it comes to horses there is what I think is fast, which is how it feels on the training gallops every morning, and there is actually fast — the speed achieved by the 1 per cent of thoroughbreds who win races out of the 1 per cent of thoroughbreds who reach the racetrack.

So I think Darcy is fast but then I get to Lingfield early one morning, as the course officials are preparing for the day and the lorries emblazoned with names like Godolphin are pulling up at the back of the stands and a few stray spectators are drifting about.

And before the track has a proper race on it, I get to gallop Darcy almost for real. She seems to know she is somewhere significant when she comes off the lorry. She jogs behind her stablemates on tiptoes along aisles marked out with white racing rails until we come to the pristine beige all-weather track, which is so wide and long it seems to go on for ever.

We do a circuit in canter to warm up and the trainer explains the plan. We will canter to the starting post, then begin to race each other. I’m to stay at the back with another jockey alongside me who will tell me what to do as we go along.

Everything is fine in canter, until we come to where the ‘race’ starts and then the other horses suddenly find sixth gear. And the jockey alongside me yells, ‘Keep up!’

But Darcy is stuck in fifth gear and I don’t see that there is much I can do about it. We are going flat out, I am told later, but I cannot believe how slow it feels. I feel like I am galumphing on the slowest horse in the world. ‘How is it possible to be going this slow?’ I think. Every stride seems to take an age as the horses in front pull away from us.

We amble along at the back hugging the inside rail for what seems like an eternity with the jockey upsides me yelling his head off about how I mustn’t let her get left behind. And I shout back that they’re not my legs so I can’t make them go any faster, can I?

Oh, to explain, something else I hadn’t realised before, you can hold very long and involved conversations while racing a horse with the jockey next door to you.

I had always thought movies like Seabiscuit were stretching credulity in scenes where two rival jockeys start nattering away to each other as they race along, but you really can do that.

I’m whingeing like mad at the jockey upsides me the whole time about how I don’t understand any of it.

And then just when I think our slowness can’t get any more unfathomable we pass a marker post and he yells, ‘Now!’

‘Now what?’ I yell back. ‘Now start passing horses,’ he shouts.

‘She’s not passing horses,’ I yell back, convinced our slowness is becoming epic, record-breaking, majestic, the stuff of legends.

‘Ask her!’ he yells.

The trainer had primed me about this. The whole point of the exercise is to see what happens when you ‘ask’ for that extra spurt of speed needed to overtake. Can the horse find it?

So I asked her. By which I mean I started doing a very strange, instinctive flapping with my arms and legs until I felt like a turkey and within five seconds my limbs were jelly and I had no strength left to hold me on and the only way not to fall off was to grip the saddle with my knees as I flapped. There was no doubt about it. I was doing the routine to ‘The Birdie Song’.

And as I performed this undignified dance, Darcy said ‘Oh why didn’t you say?’, found sixth gear and overtook two horses. ‘You’re going too wide!’ the other jockey yelled, as I over-steered her to the outside rail like an old granny on the motorway veering across three lanes.

We still felt like we were in slow motion as we passed the finishing post third from last. Just to reassure you, Darcy was absolutely fine. I was done in.