Wow - thanks John.

What length is the cable run?
up to 15 metres (10mm cable)

Will it be fed from a RCD protected supply?
What protective device do you plan on using (fuse / MCB etc)?
Not well up on this - was going to get a sparky to plumb it into my
fuse box - the highest rated breaker in the box is 45A so I'm guessing
he will fit a separate 60A breaker/isolation switch or whatever is
necessary

What earthing system does your house have?
I have no idea. I thought all houses were earthed the same

Given the above you can work out the prospective fault current at the
shower and hence the disconnection times, and you can also check the
earth fault loop impedance. You will also need to check the maximum
voltage drop is not exceeded.

Okay, now I'm lost.

You need an isolation switch - preferably in the same room but not
somewhere that can be reached from in the shower.
I was going to fit a pull switch isolation switch in the bathroom
which cannot be reached from the shower but through which it's mains
supply will obviously pass.

You suplimentary equipotential bonding will need to be up to scratch
unless you plan to implement 17th edition style 30mA RCD protection for
all circuits in the shower room.

Meaning?

Thankyou for the advice - although you've lost me a little on some of
this