I think it's fine and creative Chris. I'm still not so sure that you won't have deformation problems down the road once something has been sitting on it for a while, but then the shelves probably didn't cost all that much anyways. I don't know how it works over there where you are (England?) but sometimes you'll find that various lumberyards that display kitchens and baths, and for that matter places devoted to kitchen and baths or countertops, have stuff that that's been discontinued and moved into the warehose. So, for example, you might run across things like synthetic granite tops, Corian, or something else that's going dirt cheap.
"I've found that when you want to know the truth about someone that someone is probably the last person you should ask." - Gregory House