In reply to Sleepymouse:
This is the closure (perhaps also the 'internet says' that maybe-si mentions):
https://www.stwater.co.uk/our-visitor-sites/upper-derwent-valley/udv-route-...
I don't know, but personally wouldn't chance it while there's likely to be felling going on. I think the ideal opportunity to cheekily dodge the fences and do it anyway has just passed.
If doing all the ascent/descent in one go doesn't mess up a training plan, one alternative might be to go directly up to Lockerbrook from Fairholmes, down through either Hagg Farm or Rowlee Farm to cross the A57 and then loop around the far side of Ladybower instead.
It's a less attractive proposition than Derwent & Howden tbh. Perhaps a loop around Agden, Dale Dike and Damflask reservoirs from Low Bradfield might be a better alternative. (Muddier and more 'peaky' in terms of ascent/descent than the upper Derwent, but lovely.)
Or maybe even two laps round Damflask and one around Agden? (It's a figure-8 from Low Bradfield, so you could do Damflask one way, then Agden and then Damflask the other way for variety.)