In reply to Malcolm Tucker's Sweary Aunt:
> I've got a brilliant drill - lent it to me brother...
Are you using a decent masonry drill bit as mentioned above - that is more important than the actual drill being used in regular concrete.
> Have to admit, I'm wary of cracking the pan.
Do not drill with the toilet in position!
Place the toilet in position temporarily - mark where the drill holes need to go, either by using a pencil or tapping a nail gently enough just to mark the concrete.
Move the toilet out of the way and then get drilling.