Can I tile directly over Artex?
It's basically plaster, so unless it has a bunch of water damage or hollow spots, which you should easily hear by running your hand over the surface. I'd go with tiling over it, since the bond is just as good as plaster &amp; people tile over that daily.

However, not knowing its porosity you should first apply a Thin-set Bonding Agent. The Artex or similar product has lasted this long in a wet environment, so I think it's proven itself extremely well. What you may not realize is that your plasterboard behind the Artex also quite likely contains asbestos. So, leave well enough alone &amp; finally add a locking layer that doesn't have asbestos.