Locked in a branch of Waterstones? I can think of worse places to be. At least you'd have cultural sustenance (a plentiful supply of books), nutritional sustenance (courtesy of Costa) and lots of toilet paper (Dan Brown novels).
That said, I'd much rather be locked in any of these bookshops instead, all of which feature in Jen Campbell's The Bookshop Book. Nice to see that Northumberland institution Barter Books features - and quite rightly so.