The knees felt OK, but rather than hammer them I went to the park to meet the not-quite-a-club and ran Porter Clough and back - via a few extra hillocks. The ascent time was unremarkable and not as good as I was doing 18 months ago. As I'm 'injured' perhaps that's not surprising. The new segment history tool on Strava is great for showing progress, or lack of it.
The icy weather had made the grass into a forest of silver shards which cracked as you ran over them. There could have been some lovely photos but I was travelling light. (The local Parkrun had been cancelled due to hazardous conditions.)
I was very careful on the steep descents (that means slow) but tried to be speedy and precise on shallow gradient. I also noticed that I was being lazy on ascents and then worked to lift my feet a bit more. It felt better.