From the Glass code of conduct ...
"
Keep to the defined track. Detour only to pass immovable obstructions. Report any obstructions (including low branches) to the highway authority and the local GLASS Area Representative. Be critical of your own abilities and equipment when assessing an obstruction; it is your right to abate a non-lawful obstruction, but do not commit yourself to a bigger task than you are equipped for."
First point ... Technically chainsaws are not 'normally carried' by most people so shouldn't really be used. Nothing to do with legislation of chain saw use, you can do anything you want in private hands, but not necessarily in public places! If you're employed to clear a lane then you must have current tickets to cover liability and authority clearance before you do anything.
The general consensus is that you can abate (Move out of the way) any non-lawful obstruction. I take non-lawful obstruction to be anything that impedes progress along the lane and is usually things like boulders moved by a farmer, for instance, or a man-made barrier. Fallen trees, arguably, might not be 'non-lawful obstructions', it's not been tested in court as far as we know .. You must use some discretion here .. My reading of the legislation (Personal opinion) is that if it's not lawful to block a lane then any blockage on that lane is non-lawful so might be (abated) moved aside with tools normally carried ... That means if you come across a tree blocking a route while out laning then if you can move it, all well and good. You can't just chop it up and use it for firewood, and you can move it only far enough to clear passage, ie throw it to one side or the other or drag it to some place safer if in a gulley for instance.
If you elect to turn around and report it to a local authority, then that should be the end of it. You should not go back 'properly equipped' to clear the obstacle, chainsaws or not!
A quick rule of thumb for me is that I carry a small hatchet and a Bow saw/pruning saw .. along with the winch that's all I'll use to abate an obstruction, nowadays before anyone says anything!!
However, if there's a few of you, each with a small saw, that's a lot of potential ...