Bit of an update in case its any use to other runners.
My calf problem was down to running in snow drifts and cleared up really quickly with a bit of rest and running on easy surfaces. I then continued to struggle with lower back pain, tenderness at the back of my right knee, tight right calf etc whilst running up hill and very painful left knee when running down. I decided to go and get some professional advice and went to see Dave Jelley of Ripon (and Jelleylegs.co.uk) who is a really good ultra runner and physio.
He did some massage, a thorough assessment and even took me running whilst his son videoed me so that we could see what was happening. He has confirmed what I suspected which was that my sprained ankle has caused me to lose a lot of strength in my left leg again and the muscles are quite wasted in comparison to my right. I also roll my foot inwards astonishingly on that side, I was quite shocked. My right leg is probably compensating and getting tired quickly and I need to stretch to help the sciatic nerves in that leg (or something like that). He is going to put together a short programme for me to follow with some strength work for my left leg and some stretching for my right leg (obviously doing it on both sides) but I may have to get an orthotic for the left foot further down the line.
Anyway, he also was able to advise me on my running style and point out things to consider when ascending and descending. I do feel really positive about getting strong again and I am looking forward to enjoying my long distance runs again instead of just enduring them.
If anyone is in the area and needs to see a physio, I can thoroughly recommend Dave.