Is there an easy way to find out if fitted tiles are ceramic or porcelain?  The tiles are fitted to a bathroom wall and my daughter wants an extractor fan fitted. I believe that if they are porcelain they are a bit of a nightmare to drill?

If you have loft access, a ceiling mounted fan would be easier.  In fact, a decent mixed flow fan in the loft, and a ceiling grill is best.

Drill tiles can be hit and miss.  If they're hard, you are less likely to damage them, but will take a good while.  Keep drill cold with mist spray, and clear out dust regularly.  Once through tile, don't use any water, it will bind.