Hi Tony,
I cut down two apple trees in my back garden using a powersaw kindly lent to me by next door, I have no idea what it was called but was made by B&D and looked rather like the scorpion saw with a bigger blade.
It was ok on the thinner branches, but anything over a couple of inches thick was seriously tough going and gave me a shocking case of white-hand. Going through the trunks was like a trial dreamt up by one of the more sadistic Greek gods.
For the tree in the front garden I bought a Bosche electric chainsaw from BargainCrazy (for about £50!) and was astonished at how easy and safe it was to use. I cannot recommend a chainsaw enough for cutting thick stuff - just apply a little common sense and it's completely safe.
A friend of mine tried to do similar with one of those reciprocating 'Sabre' saws - didn't have much luck apparently.
Hope this helps,
V.