You were "stopped"......... you shouldn't have been cleaning them in the first place

Your initial risk assessment should have picked this DANGER up, which I guess from your post you never did one
and Im not too sure how i would be able to control the risk of a pole falling backwards into the roadway and catching a powerline on the way down. Did you only realise this once you were stopped?
Did you not think at all that WFP would not be the best method here?
Did you check that your PL insurance would cover you for the close proximity danger risks.
Did you actually think If I hit one of those cables, what the consequences would be for maybe 1000's of people?
I am sure that the council will want full RA's and MS's if you apply for the permit (by the way the £120 is not the main issue here) and they damn well should too!!!I really think carbon poles are the least of your worries. :

As Sean said I think they have done you a massive favour, before a major accident does occur.