They can be seen most mornings — early mornings — at the Monad Shoals, off Malapascua Island in the northern Philippines. The vertical wall, with a convenient viewing point 30 metres down, provides a convenient cleaning station for the graceful beasts with the elongated tail flukes. Johnny and the Varmints hitched themselves to the guide-rope.

The small island of Malapascua lies a 40 minute boat ride from the northern tip of Cebu, which itself is 200km from the international airport on the southern tip. The journey between these two points can be covered by a rental vehicle, either a car, van or in our case, a float plane. Never assume that the fastest vehicle will be the most convenient; we had arrived at the fag-end of a typhoon so adjustments were necessary. As it turned out, including the plane, the poor weather meant we utilised nine separate modes of transport to reach our destination.

For the final leg the dive centre sent its boat (there is a public service but it was now way too late for that). We made a night assault on the beach and I and the kit was dragged round to the shop. Johnny’s hotel was next to the Fun&Sun PADI centre, one of several dotted along the fine sandy beach on the southern island coast. An idyllic setting for grown-ups but never less than challenging for wheelchair users. Luckily, son Ryan would be at my side throughout the adventure.

To visit Malapascua from the UK and return after only four nights may seem an odd use of one’s time and money. But Ryan was joining Cheryl, his girlfriend, for a family reunion and a subequent invitation to me seemed too good to turn down. I love my diving; I knew this would be difficult but was also confident there would be plenty of willing hands.

Our programme began the next morning, bright and early. The boat’s ever-resourceful crew would experiment with ways of getting me on board from beach, boat or ocean, before settling on a plastic chair lashed to a pole and hoisted by them onto the fore-deck.

We made several dives during the build-up to the thresher descent; one to the small marine reserve of Gato, where we swam through a tunnel that was long enough for us not to be able to see the other side. It took a small leap of faith to make the dive into the abyss but it was probably only half a minute before the pale blue exit hove into sight.

And thrillingly, there were white-tipped reef sharks! Several of them, more of a conventional shark shape than a thresher and more menacing for that. By the time we saw them I was clear of the swim-through but others behind me inadvertently hemmed one in, and it darted towards them before finding a way out.

But the threshers were the highlight and they didn’t disappoint (video by Warwick Ngan Kee. The shadow at the end is of the diveboat, 100 feet up). As we were deeper, our sightings were limited to appearances through the gloom. Later there were arguments about just how many we had seen — several in succession or just one swimming in circles? Their mouths, while the familiar sickle shape, are far too small to pose a threat. But sharks of any kind have this mystique and thresher tails, which they use to stun their prey, are especially impressive.

Again due to the depth, our bottom time was limited and we needed to make a decompression stop while surfacing. On our way back to breakfast we were an excited group.

I always enjoy night dives, from the tip backwards into the blackness to giving the thumbs-up signal and piercing the silver surface above. And you always see good stuff; to improve my chances I tied a torch to my mask strap. This evening’s highlight was a writhing mass of green and black sealife, presumably feeding on some corpse, looking for all the world like the fabled snakes on Medusa’s head. They looked like eels but I later learned they are a type of catfish.

Now, back in England, having spent most of the past week either in the air or under the water, I feel a sense of accomplishment. I also feel shattered, which is odd considering others were doing most of the hard work. Would I go back? I initially thought never again. But on the other hand the hotel quickly put up several ramps, one permanent (Ryan christened it before the concrete set). I eventually found an almost sand-free route between the hotel and the dive school (the FreeWheel was again invaluable). The chair device works, although we must have stressed this particular one to its limits. And I finally made it into the shower without Ryan’s help (the exiting manoeuvre requires more thought).

So, with all that infrastructure now in place — madness not to, really.