It's gone! After a couple more sessions of cutting it as low as I could with the loppers I went out this afternoon to finish the deed! I had a long handled sharp spade, a border fork and me trusty loppers (and a very tough pair of gloves!). I removed the remaining dross from the far side (the side I've never been able to reach before!) and found a slumbering tiggy, which I covered up again with plenty of dried stuff. From the side I could easily reach I started to chop at the roots under the clump and then sink the fork into the centre and lever it about till I heard roots tear. I removed a bit at a time like this - some of it I practically unscrewed! However, only fibrous bits of root are left and I can't see it coming back from those - especially when covered in daleks full of compost. Thanks to everyone for their advice and encouragement - except the bit about the swingers!
Wish I hadn't known that!
