Does having 300mm attic insulation in the attic mean the end of attic for storage?

I'm considering adding extra insulation to my attic. At present there is 100mm of insulation. This is a single layer rolled out between the joists (which are 100mm deep and 400mm apart).
If I cross lay 200mm of extra insulation on top of this, doesn't it go without saying that I will no longer be able to use my attic for storage? Unless I have some sort of a shelving system close to the entrance, or a hanging floor above the insulation.

Thanks.

We have put insulation down on top of the attic floor. Its like a 4 inch thick very solid polystyrene and I have walked on it several times. The people doing the insulation suggested this material. Under the floor had already been insulated with the usual roll out stuff and that was left in situ. We store some things on top of it like Christmas decorations etc.

MY attic was already insulated when I bought it but it seems to be 4 inch solid polystyrene with boards on top of it. It's grand, no storage issues

We did the same, and put some solid polystyrene sheats with plywood backing on the joists for storage. I can't find where we bought them , but I think they were kingspan or similar. They can be cut to fit the joist gaps so that they butt up against each other while their edges are resting on the joists.
Just one thing to remember - make sure all electrical cables are brought above the boards, as the polystyrene will eat the cable sheating, as well as insulate the cables causing a fire risk.