All British chain book stores, Borders, Books Etc, Waterstones (incorporating Ottakars) and WHSmith, have about a shelf and a half of Star Trek books, and most of the independents carry none. The only place with a large collection, ie more than a shelf and a half, is Forbidden Planet.
my local WH Smiths don't stock ANY Trek or Wars novels. the best you get is some Bear, Pratchett and Eddings.
the local indie bookshop however, will order in anything you want and, last i checked, had a case of mixed SF&F. mostly old Trek and Wars and Original SF&F