Back at NH,
I'd recommend starting with the handling agents - we've had several problems with them before on flights from Germany. I'd reckon the best place to start would be with the handling agent in BHX (I think it's Swissport), I might be totally and utterly wrong on this though, as they will be able to track down the bags and put you in touch with the German handling agent in turn.
Sadly, I've learnt the hard way - having lost a bag with a whole load of skiing equipment on it, I've always found it a lot easier to speak to the handling agents - it cuts out the middle man.
Sorry if it's not much use though, it's just the best I can think of right now...
Cheers,
AD