It was a relief to actually start our expedition down Titan, Britain’s deepest cave shaft. It was an even bigger relief when our leader Tim announced the plan.

“I think we should ascend back up the ropes once we reach the bottom, rather than doing the Titan through trip”.

“Thank god for that,” I said.

I’d been fretting all week about swimming through freezing underground lakes and squeezing through tight passages.

Harnesses over waterproof suits, thick socks inside wellies, the five of us headed across fields laden with big bags of rope and smaller ones of flapjack, flasks of tea and spare clothes.

We gaped in awe as Tim unlocked and swung open the metal door to reveal the first shaft. It was like staring down a long gun barrel carved of rock. A 170ft abseil and a crawl through knee-deep water along a horizontal passage lead to the edge of the 460ft Titan shaft proper. My feet were sodden already, but I hardly noticed.