Well did a test dig this morning, marked out 1m x 1m in the furthest corner (so SWMBO doesnt get too upset lol) and got a "grub mattock" from B&Q. For those of us of a "gardens are somewhere to look at and sit in" persuasion, this tool is a revelation and great fun to use, until your arms get tired that is... makes short work of roots and anything else (well ok maybe not the 3" ones) and makes it very easy to lift the result with a spade...very quickly took off the top 5" or so apart from two 3" dia roots that were just under the surface... I'm still amazed how much spoil comes out of such a small space !

Looks like I'm going to hire a microdigger and powered barrow for delivery Friday morning, that gives me most of Friday, Saturday and Sunday to dig it out and get the spoil to the front garden, grab truck to retrieve it on Monday.... at least thats the plan...