Hi Alice
I donate to chester though there is another bank closer (when I started my ds was older than they like, though now both will take milk till your lo is 1yo).
I found them through the UKMBA website.
I had some blood tests at my gp using stuff the milk bank sent. They have lent me a pump and sent everything else youu need (bottles, pens to write on them, temperature record charts for youur freezer, thermomiter for frezer, and a mug for tea!)
I pump, name and date the bottle and freeze. They collect every month/5weeks or so.
There are some criteria such as not drinking more than a couple of units 2x a week and I think not smoking (thouugh don't recall quite as don't smoke any way...the drinking stands out as I'd just got my appetite for vino back when I started donating! Typical! Hey ho, it can wait!)
Erm, think that's it...anything else? 
No doubt lots of people will have replyed by now as I stopped for tea!