I've just remembered, You can skimm over it with plaster though, less messy and more expensive, unless the Artex is holding the plaster together underneath.
Hamish
I have come accross a wonderfull product called X-Tex. It is safe to use as it doesnt contain any nasty solvents. I applied this product to my Artex in the kitchen, left it overnight and clean it all off the next day. It didnt even effect the underlying plasterboard.