I read that hedgelink brochure and it may do for large concerns but we have found different here. The main reason the bottom of our hedges were getting gappy was the ruling that you could not spray out the vegetation underneath. All this lovely lush growth outdid the bushes for light and the bush then sent all its new growth up to the top and became thin and straggly down below. Some land not in a "scheme" we kept clearing out the undergrowth and with exactly the same management otherwise within three years the difference was really noticable.
Now all our hedges are not covered by any scheme regulations (over a third of a mile) they have had a major trim, but not extreme, and are trimmed back every year. The sheep clean out the bottom and they are thickening up again. The hope is to get two trims in, weather permitting next year as the section of hedge that we have done this to is massively improved again.
Another bonus for us is that by trimming regularly there is not any really thick stems and so the tractor needs a lot less passes to get the growth back down, this reduces the damage to the land alongside the hedge.
We charge £25/hr