Officially I dont know, just that no shop has any on the shelves and no online place I have checked has any new copies in stock.
This is a common problem for all bookshops today. With shelf space at a premium, and store managers knowing that so many people now order specialty lines via online shopping, the random browsers wandering into bricks 'n' mortar stores are setting themselves up for major disappointment if they only check the shelves and wander out again, empty-handed.
Chain bookstores often have computer databases that show stock, not only on their own shelves and back rooms, but the shelves of other stores owned by the same company. Asking at the front desk, they can sometimes quickly tell you how many books of a title are on their own shelves, awaiting unpacking, at the warehouse, on order, and in stock at other nearby stores.
But you must first ask.
When TNG was at its peak, many bookstores took an opportunity to stock their shelves with two copies of every ST novel then in print. I think Pocket was offering some kind of deal on a mixed box of back titles. Something similar may happen if JJ's ST film takes off in a big way. (Although, when Season Three of TNG started to do so well, at least the shops had a projected window of about two years to shift all that back stock. These days, many shops want all stock sold and gone for a title in just a few months.)
I may try placing an order with Waterstones in town though, see if they can find it.
It's highly possible the book you want is sitting on a shelf or in a UK warehouse. Your Waterstones should also list the stock of other Waterstones.
Until you make that request, how does Waterstones know they're losing your money by not restocking "Cathedral" or "Lesser Evil", books that may last have been orderered in 2002? (And which are still on the shelves of several bookshops here in Sydney. We even have a few copies of the first two MMPBs!)