I am thinking of having a second storey extension built on top of an
existing extension. The problem I have is that I don't know what the
foundations are like on the existing foundation to see if they will support
a second storey.

The local Building Control department have told me get a Trial/Pilot hole
dug and they will come out and inspect the foundations.

I have been told the make sure the hole is on one of the corners of the
existing extension so that both sides of the foundations are exposed and
visible.

As I have never done this before, can anyone suggest the best way to this,
what to do and what to avoid, any pitfalls to look out for. Do I need to be
a set distance away from the walls?

I assume (on the basis the ground id sodt enough) a spade and the likes will
do, i.e. no drill/diggers required

Any comments appreciated
M