Just a general comment - as I know nothing about legal procedures...
I agree with what I think BankFodder is suggesting - it really ought to be a straightforward question of a breach of contract. You've paid for a service and the other party (or their sub-contractor) has failed to perform that service - safe delivery to the addressee. It seems daft to me that the risk of non-delivery gets passed back to you because you've not paid for insurance against their failure to perform their responsibilities. It's an inherently unfair* business model that has crept up by stealth, assisted by the growth of internet shopping. Of course, a court may not agree...
I also agree with BF that you should be able to do some research yourself, and you should see this as an opportunity for self-directed learning as well as self-help! You can always check back with BF, Andyorch and dx100uk that your understanding is correct. You might get some ideas for final year dissertation - it's a bit of an academic problem with real-life commercial implications.
*Of course, in the absence of this business model, courier fees would go up, but I would argue that's a fairer way of spreading the risk of loss/damage etc
(PS - I was a law student a looooooooong time ago. In your position I'd have tried my tutors as a sounding board as well. I also thought SBU had it's own law clinic - although the advice is likely to be quite basic unless somebody sees this as an "interesting" problem)