I had another chat to them - they are so nice

They said the amount doesn't matter and they will give me bottles to put it into which I need to label up with name and date expressed. As it is pasturised, they said you can top up milk that you've expressed and frozen with fresh stuff to get a full bottle if I want to do that.
The blood test is just for the usual checks (very wise). Mike laughed and said couldn't they just look at my notes from my pregnancy as they seemed to forever be pinching my blood
LOL!
Sophie feeds every 2 hours during the day but she's asleep by 8pm every night and goes through so I have time to express some more and it will just bring my milk supply up a bit. I expressed tonight at 10pm and got 3oz from one boob so I think I'll be ok to give them a bit.
Funnily enough, I didn't know about these things before but I've just started helping out my local NCT doing their website and I came across some info on milk banks and thought it was a great idea.
Also, having had Jasmine prematurely, it seemed a nice way to give something back (albeit 10 years later!)
Will keep you posted as to how it goes.