They've gone bust.
The one local to me (Bath) is currently having a 'fill a bag for a fiver' clearance sale.
I came away with close on 90 quids worth of railway books (all prototype, didn't see any modelling ones) stuffed in me little carrier bag for that fiver. ( I then sent the wife in and she brought out a bucket load more) The books are all quality stuff too, despite being remainders.
If you have one of these shops local to you then it may be worthwhile checking it out at the moment.
Pete