I've just moved into a new house and am updating the bathrooom. Whilst re-tiling the electric shower cubicle I noted that the existing wiring has been routed from out of a side wall, some 18 inches away from the shower, and then through plastic capping/ducting across the tiles (externally) to the shower itself. Is this:

a. Legal?
b. Safe?

Unfortunately the shower cubicle has been aquaboarded and replastered so am loathe to rip the wall out to re-wire unless I have to. I would appreciate some advice.