Basic rule of thumb for buying from the UK:
WARNER/PARAMOUNT - fine.
SONY/COLUMBIA - fine except for one or two early day-and-date releases before Sony dropped Region coding in Region B altogether (Click and i think Monster House were the only ones region-coded)
DISNEY / BUENA VISTA - fine for catalog releases, avoid day-and-date (Hollywoodland, The Guardian, Deja Vu etc.)
FOX - avoid, almost all discs are region-coded.
Same goes for buying from Australia where discs are often cheaper than in Britain incidentally, hope that helps you!