Thanks all for the advice. Ill paint it over with standard emulsion for now.
Its not a big bathroom so if I get problems I can always repaint it. From
looking at the product descriptions it looks like the paint mainly allows
you to wipe it down say it you got some sort of stain on it. Also, thinking
about it, most people don't do the ceilings with bathroom paint and rarely
get any problems with them and this must be where most the steam will
collect.

I've also got an extractor fan and I can open a window to alleviate most of
the steam.

Cheers,

CM.