In reply to TheDrunkenBakers:
If they're not yours, they're someone else's. I would imagine that if they're someone else's and you cut them without permission then that is criminal damage, and that if you remove them from the site without permission then that is theft. Although the waters muddy if its a species the land owner has a legal obligation to control.
So talk to the land owner! Perhaps they'll embrace the offer of removing them, perhaps not. Better to be told "No" in advance than to have the fuzz turning up after the fact.
Just cutting rhodadendrum away doesn't clear the infestation (more drastic, chemical measures are needed) and for all I know (or don't know) cutting it back may just encourage more growth? Plenty more here
http://www.forestry.gov.uk/pdf/fcpg017.pdf/$FILE/fcpg017.pdf
I think it's vile stuff, but I'd be wary of just taking a saw to someone else's wood. Even if they are in principle happy to see the menace go, there are all sorts of reasons (liability, encouraging other people to help themselves to other wood etc) they might not want you to.
I think that theft of wood from private land is going to become an increasingly prominent issue with the rise in fuel costs and the rise in popularity of wood burners.
Post edited at 10:28