On Fri, 08 May 2009 13:20:57 +0100, Andrew May wrote:
If I get a chance I will dig some more over the weekend. If it is a
septic tank then it should have a solid base at some point and I would
like to find it.

This is where you find a sodding great wartime air-raid shelter or other
such structure :-)

(have Google or any of the other imagery services got high-res data for
your area? A look at the lawn from above *might* reveal discolouration if
there's anything just below the surface there)

cheers

Jules