Indeed I am in the UK ... London, Earth ^ up there
and indeed - a good size and material for your project and a very good price. The two hemispheres are joined by a fold on the outside creating a rim round the middle but you could cut this off easily enough. It's an end of product line from what I can see.
If your local woollies has sold out you you can buy one online here +£5 for postage.
CrazyB
im planning something similar but instead having the inside of the case looks like the inside of a borg cube...with regeneration alcoves and stuff