Pete wrote:
Any suggestions for better methods would be welcome - particularly if
someone knows where I might hire a hole cutter big enough to do the
job! (I live near Norwich, just in case anyone knows anwhere local to
me.)

Thanks.

I certainly would not lay out £90 to hire a tool thats going to be used
once in an hour. :-(

I would cut a square to the diameter of the circumference, fit the pipe?
and the fill the four corners with cement pushed in with a stick till it
was solid packing.

--
Sir Benjamin Middlethwaite