Advice on root boring tool

Stump grinder. Costs thousands, but you can hire them.

Otherwise a mattock, and sharpening its edge (ObAngleGrinder) beforehand. You can also drill with a spade bit or auger, then use this access hole to burn them out.

One method that I've used where access is difficult is to use an ordinary twist drill intended for metal to make multiple holes in the root. The drill can be rocked on an axis perpendicular to that of it's rotation to join adjacent holes as much as space permits and generally weaken the root.

A good old fashoned crowbar with a reasonably sharp chisel end can then be used with long stabbing strokes to further sever the root and then used as a lever in the usual way.

An SDS drill fitted with a chisel bit eats leylandii roots for breakfast. (in hammer mode with the rotary motion turned off)

Something like

An auger could make lots of 1" wide holes.

NT

Felling axe?

Thanks for all those ideas. The multi-£grand machine is OTT for me and the suggestion to use large metal drill bit idea came closest to what I had in mind. I just found a reference to this tool and may give it a try:

Think I'd stick with the auger.

NT

Yes, worked well enough for me. The bits tend to bounce off the softer roots but they get through in the end.