FunkyDoc, I faced the same dilema with my girlfreinds garden. Bloody laylandii all the way round the house. Must have been over 200ft of the stuff and at least 15ft tall.
I had a good set of hedge trimmeres which are fine for taking the sides back, but obviously no good for toping them. The Branches ranged from very thin to around 3 inches thick or more. I started out with a saw, but after a few days I was getting nowhere and my arms and shoulders were done. So I bought an electric chainsaw. Far better than the petrol one I had borrowed in the past, It felt much safer, easyer to use, lighter, didnt have to **** about with fuel etc, BUT it was usless on anything less than about 2" thick as the branches would just bounce off the chain. Chainsaws arnt much good on thin stuff that isnt held firmly in place.
Leylandii typically being a cluster of thinner branches ment that the chainsaw just wasn't any good for trimming the tops down so I went back to the drawing board and picked up one of those Black and Decker Aligators. Its bloody fantastic! The jaws will grab a whole bunch of branches of any size together holding them firmly whislt the chain slices through with ease. Its far far safer than a chainsaw as the chains pretty much always gaurded by the jaws. Ive lent it a few mates in the past and they've all gone out and bought their own afterwards.
If you live anywhere near manchester, or more specifically salford keys, there is a Black and Decker outlet shop in the Lowery center that are selling them for £35 with a two year warranty. Bargin!