In reply to Ste Brom:
I'm familiar with ITBS from cycling, and this is quite different (a much sharper pain deep in the joint), may give the roller a go though just in case.
In terms of shoes, I used my normal approach shoes - probably a bit heavy, but never had any problems walking long distances (with a pack on).
I do have tight hamstrings though, so perhaps some stretching will help.
I did have an issue with the other knee a few years ago which was put down to a torn meniscus from playing rugby... this feels vaguely similar although it hasn't locked