I guess this is asked a lot, so please point
me in the right direction.

I want to drill some holes in large bathroom tiles,
to take screws for a grab bar in a shower.

I've been advised to buy a drill bit specific to this task -
what should I ask for, and what is different about these bits?
I'll be visiting South London Power Tools, which seems to have
a great range of these types of things. I'd like to display
some knowledge of what I'm after though!

Also, what sort of wall anchors are recommended?
The tiles are on the side of a shower stall, which is probably
made of plasterboard underneath.
I've got some spring toggles and some other expaning wall anchors.