I set off at about 11.45am from the youth hostel at Pen-y-Pass for solo ascent or partial ascent of Glydr Fawr by the ill-frequented route past Lyn Cwmfynnon, up the south ridge of Glydr Fawr. It was very windy and the ground temperature was lower than the day before, so that I thought there could be ice patches nearer the summit. I did not have crampons with me and told myself that I would simply turn back if it got too risky. However, I did have plenty of clothing, an ice-axe and a group shelter, good headtorch and spare batteries plus food and a hot drink in a flask. As well as paper map and compass, I had OS maps with the relevant area downloaded on my phone.

Mindful of how cold and windy it was I decided to put on my down jacket right at the start of the walk so that I was wearing all my layers (merino top, two fleeces, down jacket and winter waterproof as well as overtrousers, gloves, hat and buff). This turned out to be a good decision. Although I was sheltered from the wind for much of the ascent, I didn’t feel too hot even with all those layers on. There was a thin covering of new snow from Llyn Cwmffynnon upwards and higher up some patches of deeper snow. In the unsheltered parts there was spindrift so I put on my goggles.

As I got higher I thought about retreating a couple of times, partly because of the wind but mainly because there were wind-blown patches of snow and frozen ground that were very slippery. I thought I could circumvent these. At one point I actually did turn round for a few metres before changing my mind. Eventually I found I was less than half a kilometre from the summit and decided I might as well go for it. I can’t remember exactly what time I got there – I think it was about 2.15pm, which was a bit on the late side given the time of year, not leaving much room for manoeuvre if anything went wrong.

I had seen no other people on the way up and at the summit it at first seemed there was no one else on the whole Glyder range, then I spotted two people about half a kilometre away heading towards Glyder Fach. These were the only other people I saw on the entire walk.

Glyder Fach looked temptingly close and I headed towards it for a few metres, then, aware of how rough the ground was, decided that it wouldn’t be sensible given how late it was, and that it would be better to retrace my ascent route. The spindrift seemed to have died down, so I took off my goggles, but the wind whipped away the plastic bag I was keeping them in. A couple of minutes after that, before I’d started my descent, I slipped on frozen ground and twisted my left leg, which was painful. It was soon clear that I’d sprained my ankle and lower leg quite badly. I rested for a couple of minutes until the initial pain wore off, but decided I then needed to start my descent forthwith. Walking was difficult, however. I didn’t have trekking poles and could only use rocks (where available) as a handrail and my ice-axe for support where there was a slope. After a while I found I could only walk a few steps except on fairly level and smooth ground and so I moved on my backside using my good leg and arms to perambulate wherever there was a downhill slope.

I never thought of trying to attract the attention of the two people I’d seen (who were far away and out of sight by now) or of phoning anybody. I didn’t even check that I had a signal. With hindsight I should have tried to phone the hostel to let them know what had happened and to ask them to call the mountain rescue if I didn’t get back by an agreed time. Before setting off I'd called in the hostel (where I was staying that night) to drop off some luggage. I mentioned in passing that I was heading up Glydr Fach, having for Fach and Fawr mixed up.

Although I had 600m of descent and only about two and a half hours remaining, I was fairly confident I could make it down, albeit after nightfall. As I had downloaded OS maps on my phone and could see my position from GPS, I wasn’t worried about navigating in the dark.

I found moving in the makeshift fashion I’d devised wasn’t too difficult. What was more difficult was to find the right route, or more importantly to find a feasible route. There were steep crags in various places and localised ones even on the part of the ridge that was negotiable. Because of my method of locomotion, however, I needed to descend directly wherever possible rather than following the exact route I’d ascended. I judged it quite well most of the time, although there was one point where I had to retreat from the edge of a crag and find a different way.

Clearly I was moving much more slowly than walking pace, but it was difficult for me to judge just how slowly. I seemed to be making good progress, but became a bit disheartened in the final part of the descent towards Llyn Cwmffynnon, when it was getting really dark and I lost sight of the faint path leading from the lake down to Pen-y-Pass. By the time I got past the lake the stars were out. I tried to follow the line of the path as I remembered it, but a bit later, when I checked my position on the phone, realised I’d started to descend too early. I briefly tried re-ascending to regain the path, but this proved too difficult, so I decided just to keep on descending towards the road a little to the Llanberis side of the hostel, even though I could see from the map that there were crags in the way. Luckily I was able with the aid of my headtorch, which I now switched on for the first time, to make my way through the rocks to reach the road about 150m from the hostel. Just walking that short distance was not that easy. I reached the hostel at 6.45pm. The descent had taken me about four and a half hours compared with about two and a half for the ascent.

When I got to the hostel I was offered an ice-pack but declined it, thinking the injury was not serious and I would be much better after a 'good night's sleep'. Next day I got to my home in London using public transport. I did not see a doctor until eight days later and did not get my ankle x-rayed until three weeks after the incident, when a private physiotherapist said she suspected I might have a minor fracture. The x-ray was inconclusive about that.