The ceiling is quite high (thus the false T&G ceiling presents no
problem), it's distinctly more than the normal modern house ceiling
height.

The exact height of the ceiling is very important in determining the answer.
Can you measure it? It will reflect on which zone the ceiling is, in various
locations. The zone determines the IP rating required.

If we can assume that the ceiling is between 2.25m and 3m from the floor,
then it will be Zone 2 above the bath/shower, Zone 3 within 60cm of the
shower/bath and unzoned more than 60cm from the shower/bath. This means you
need IPX4 (where X is any number) fittings right above the shower/bath.
However, outside this area, any fitting can be used, provided you don't
intend to use a hose to clean your bathroom. If you do intend to use a hose,
you must use IPX5. IPX4 means splash resistant. IPX5 means resistant to
water jets.

As a minor additional question what sorts of lights and switches can
one have above a washbasin, are only pull switches allowed for such
lights? (It'll be pretty close to the bath, it's not a big bathroom).

If it is more than 60cm from the bath and shower, there is no blanket
requirement to use pull cord switches or use special light fittings.
However, there is a general requirement to use switches and luminaires
suitable for their location. Having a live switch right above a basin might
not be considered a good idea. I've heard 30cm being considered a rule of
thumb to determine how far from a sink an accessory should be installed.

Christian.