you could buy a drill tip from B&Q but if you have not drilled mirror before risky. you can also buy mirror clips from such as B&Q that drill the wall then hold the mirror without drilling the mirror.
Another method use mirror adhesive and glue it to the wall.
or take the mirror to local glass merchant who will drill it for you for a small consideration. but if it breaks the risk is usually yours.
If you do attempt to drill holes, you will need (as well as using the right bit) to keep it lubricated with oil or paraffin, inside a dam made of Plasticine.
But I'm inclined to agree with John, it's best avoided.
An alternative to using metal clips is to make rebated wooden pieces to hold the mirror at top and bottom edges, and screw these to the wall (which is the method I prefer).
It's not me that wants the holes in the mirror, it's my next door neighbour but as he doesn't have a computer, I was asking on his behalf. My own advice was to use some clear silicon sealer as an adhesive to fix the mirror to the tiles.
I will pass on your comments but will recommend that he takes JohnD's short and concise advice.
If he doe's decide to have a go at it, I will let you know the outcome.
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