Thanks Roy,
Well, it all started well, I did my small pilot hole and then proceeded to try a larger drill bit.
Unfortunately the bit sheared off leaving it's tip in the hole.
Now I'm stumped, as it's got dark I thought it best to sleep on it and ask for suggestions.
I suppose I could try drilling around the captive drill bit with a small "super-hard" bit.
Not really sure how to proceed, any ideas welcome.
Thanks!