Try the Bathroom Fitters Kit:
Selection of seven cores in five popular sizes.
Priced at £49.99 for the kit its superb value for money.
have a look at the website:
Drilling porcelain tiles with diamond tile drill bit granite holesaws
Also there are many other size packs (37 sizes) so if you need a special size hole then everything is catered for.
Example:
Perhaps you have a mono-block or tap to install. So in that case 35mm is the right size.
In short we have every size drill bit but that multipack above gets you out of all sorts of trouble.
For example if you have a fischer fixing kit for a sink and perhaps you need a 10mm drill or a 12mm drill or a 14mm
then use the 16mm drill supplied in the kit to take a plug out of the tile bigger than the hole size you need.
Then just use a nomal masonary drill to cut the actual hole behind the tile.
Once you fit your appliance over the hole then nobody will know. Useful for things like sinks or loo pans.
Lots of projects on the website to follow too (section 4)
Stocked by retailers like Corgi-Direct plumbing and other retailers.
And it comes with the guide plate to stop drills slipping on
ANY tile wet or dry
Each kit from 6mm to 65mm comes with a guide plate to stop slipping on tiles