After reading the advice of above, I've decided to give BA more time - I can't actually give them a call now as I'm outside the UK. Let's hope they get to it before Christmas I guess...

I do genuinely think that BA's response time is nothing short of pathetic, and I cannot think of another company that takes over 7 weeks (and counting) to respond to a situation in any way whatsoever (even a 'we're looking into this and we expect to reply to this within X days from now' would be something). Looking at posts on other forums, other airlines seem more more proactive in replying to customers, negatively or positively - which then gives the customer the information they need to either stop the claim or go further.