In your
back garden Flummery? I can't imagine what that says about you!!!
I had one at my last house - with the added attraction of a wasps' nest in the middle. I spent a full day running up to it, bashing it once and then running away fast.
I worked from the outer edges at ground level. Inside the vicious outer leaves I found lots of dead, dry materials that came away easily in big handfuls. Under this, the roots didn't go down far and I could cut through underneath it, finally rolling the whole clump out in one go. Not an easy job, but not as hard as I'd expected.
Some people advise lighting a fire in the root hole, but I settled for building a ten-inch thick drive over it...