11-00-01 is actually a Halifax sort code. (Halifax is owned by Bank of Scotland which, of course, has just been taken over by Lloyds TSB).
I'm not certain but I suspect that like Abbey (and other former building societies), Halifax doesn't have specific sort codes for individual branches. It simply uses a few sort codes (probably for different types of accounts) all of which are officially based at the bank's head office (irrespective of where the customer actually opened their account). If so, the address is probably this one:
Halifax
PO Box 548
Leeds
LS1 1WU
Chris