Fair play Nowty, that was a nasty problem.
Unstable ground always looks better when covered by a tarp or ply sheets

and they often do piled foundations because the ground is unstable .......
Clay is kinda friendly though and more likely to fail slowly.
I have occasionally been the wrong side of the saftey box or under a digger bucket in an unsafe trench for brief periods and its not a good feeling.
Always promising myself and guardian angels that I will never do it again and get quite carried away with my 'duty of care' if I see someone else doing it.
Enjoyed the thread. Thanks to all who contributed.