Where can I go to find definitive maps of UK council and district boundaries?

Because I've just run up against a problem where there's some fly-tipping practically underneath a "No Fly Tipping" sign. The sign is put up by one district council with one phone number but it turns out the site is well within the boundary of another district with a different reporting phone number.

If I follow this up to find the maps, I get put through to some obscure land registry department in the councils and still can't get the information. I've tried this with both district offices and the county council offices. As far as I can tell the Ordnance survey maps don't have these boundary markings either.

Meanwhile the fly tip waste is still there 2 weeks later. It's household builder's waste, some of it in rubble sacks. Why, how? It's on a Restricted Byway with quite a lot of walker, bicycle, horse traffic. And yet none of them seem to want to report it or do anything about it. So is this a society problem, council problem or landowner problem? Who's supposed to deal with it? And equally, who's job is it to maintain the track and keep the overgrowth under control?