This sounds either like a reciprical saw or a top handled chainsaw.
Both are very dangerous in the hands of untrained people and can be
fatal. Top handled chainsaws are intended for use only by
arboriculturalists after training and then only when up in the tree,
not on the ground. There is a code of practice for there use issued
by the HSE.
Alan.

Chris French and Helen Johnson wrote in message ...
In message , Nigel M
writes
Some men just came to trim a tree below an overhead power cable. They
had what looked like an electric carving knife, a one handed chainsaw.

so was it like a chainsaw or like a carving knife?

Assuming the latter some sort of reciprocating saw. It was probably
something like a Dewalt alligator saw or Bosch Tyrannosaw -these have
two opposing blades that move against each other - cutting better in
heavier duty materials than a single bladed reciprocating saw.

http://www.tooled-up.com/MicroCategory.asp?CID=4&SCID=20&MCID=585

For examples (not necessarily cheapest, just the first good link I
found)