@bobmac I hope your knee injury has improved since we last spoke.
Update from my side - I couldn’t see the ortho specialist in March, due to my local hospital being maxed out with covid patients. I wasn’t bothered, some things are way more important than cycling.
However, I found another local physio on recommendation from a friend, and his team have fixed me. The lockdown period in the UK and working from home gave me extra time to spend doing physio exercises and having remote zoom calls with him when required. It was a big commitment, 2x1 hour sessions of exercises daily. April was tough! We gradually built my training up from 3x20 mins z2 a week to 3 hours+ outside over a period of 2 months.
I started SSBLV1 six weeks ago and I haven’t experienced any issues during this period (other than an FTP drop of 20w over 6 months 
).
Thanks again for your advice, I hope you have success too.