Hi Andy, welcome to the forum.
This looks like it might help:
http://www.brdatabase.info/index.php
From the menu on the left, select sites, then depots and this then gives an alphabetical list of BR depots. Click on the depot, select the locos allocated tab at the top of the depot details & this gives a list of all locos allocated from 1948 (or depot opening if later than 1948).
Hope this is useful.
Tony