I've been meaning to come back to this for months, as I wanted to say thank you for everyone who read and replied to my thread. After almost 10,000 words on here, 15 different physios, about £1000, and 2 years, I am now back playing football, have no pain whatsoever in my knee, and although I think there will always be a bit of weakness in that ligament, I am so unbelievably happy and grateful to get where I am now.
The advice on here was really useful, especially when I was away travelling and couldn't speak to anyone about it properly, and it made such a difference just to feel that I was being listened to and to be reassured that my worst fears weren't accurate. I'm sure if I'd been able to see any of you you would have helped me recover, but in the end it was the 15th physio I came across (I got passed around a few different physios when I went to different practices, saw private and NHS physios in Manchester and London and saw a few different ones when I was travelling in Brazil, Chile and Colombia) who saw what it was that was stopping me recover and helped me through it.
Basically, my problem was in my posture. I may struggle to remember everything now, but I had over-active hip flexors and very shortened quads (I'm 6'3" and so the growth of my muscles probably didn't catch up properly with that of my bones) which meant that my hip was significantly tipped forwards, I gripped and held through my hip flexors and lower back rather than stomach and those muscles near my glut, and as I walked, rather than the pressure going through the centre of my leg, it went through the inner side and my feet rolled in, suggesting that I had flat feet, even though this wasn't the case.
The process of becoming aware of what muscles I used when I stood and walked was absolutely torturous, and changing it virtually impossible. I'm still very much in the process of changing these in-grained habits and becoming comfortable with them, but I'm at a point now where I've given my MCL enough of a break for it to recover. It wasn't without some pretty serious set-backs though, as I was trying so hard to change things that I didn't understand that I made the wrong changes, forcing movements with the wrong muscles, so that for about a month at the end of last year I suffered serious back-pain and developed a nerve problem in my left leg whereby I had pins and needles in it constantly. I nearly lost it at that point as my physio was telling me it was just because I was getting older and these things happen and I knew that wasn't the case, but thankfully my persistence, her patience and my eventually gaining the awareness I needed, paid off.
So again, thank you. A lot of your posts show that you were on the right lines, and I just wish one of the 14 other physios I saw beforehand had looked at the bigger picture of my whole posture etc rather than focussing purely on the knee.