I managed to fall off yesterday and whack the rear mech.

Can anyone help me work out whether it's the mech hanger or the actuall mech that I have killed?

When I first pushed bike after said accident it sounded like I had a twigg in the spokes, but it was the mech hitting the spokes.  We pulled it out a bit so as I could ride.  It's at a very odd angle so I've pulled off the mech and have noticed the hanger looks a bit bent.  Is there any way I can tell if it's too bent?

Why don't you ask on Singletrack or Bikemagic they will answer your query straight away.

If your shifting is crap no matter how much adjustment you give it the hanger is likely too bent.  I have done at least four hangers and they have all been terminal as they tend to twist as well as bend (or they do when I crash on them), the mech cage is also quite vulnerable though I have gotten away with only replacing the gear hanger once!

I always carry a spare mech hanger for my full-suss in my Camelbak, it lives in there permanently, my hardtail is steel so doesn't need one or I'd be carrying one for that too. 

It's a bent hanger, at least it's only £12! A lot cheaper than a new mech and ten times quicker to put on, well theoretically.

I recommend you go to your bikes dealer, otherwise they need to know the model, easy one to answer and the year of manufacture, not so easy if you're anything like me.

Thanks for your advice ladies.