The message MPG.1959057bc399c2f3989794@lateinos
from Warwick contains these words:

I wouldn't worry about ripping out an 11' one. The roots on a Leylandii
tend to become very thin and wiry within 6" of the base even on a 50'
one we took out here there wasn't much to speak of in the way of big
roots. My trench around the monster of our hedge was no wider than 2'
from the base to allow me to get the hand axe in to get those pesky
little roots that form under the base and make life interesting when
you'r trying to persuade the bugger to give way.

Leave a couple of feet of stump standing when you cut off the top
branches, then you can use the stump as a lever, which is a big help
when getting out the severed roots.

Janet.