A.Lee wrote:

But wouldnt fitting a RCD be much safer than it being protected only by
a fuse?

It should be perfectly safe without an RCD provided that:

(i) the earth fault loop impedance (Zs) is low enough to ensure that
the fuse/MCB will blow/trip in less than 5 seconds in the event of an
earth fault, *AND*

(ii) SUPPLEMENTARY BONDING is in place in the bathroom, including
bonding between the earth terminal of the shower unit (or nearby
isolation switch) and any metal water pipework, particularly pipework
feeding the taps of a metal bathtub over which the shower in question is
used.

Supplementary bonding can be omitted under the 17th ed. if the relevant
conditions are met (RCDs for all bathroom circuits including lights and
main bonding in place for the building as a whole). If the shower has
no RCD the conditions are not met and the bonding becomes vitally
important to keep the shower outlet and your tootsies at more or less
the same voltage...

--
Andy