There are a few issues here - if BT went there of their own accord, that would mean they were either telling porkies when they told the council that area wasn't commercially viable, or taking a loss on going there just to stamp out a competitor, which monopolies can't legally do.
The worst part of this is that BT not just going there, they are getting paid by the taxpayers to go there!
I met some people from "Faster Broadband for Worcestershire" yesterday, and pointed out that this was going got be unpopular and possibly illegal, they didn't seem to care about popularity, and fended off the legal issues by saying the wireless solution they spent money on first time round didn't technically meet the EU definition of superfast, so they can get away with spending our money on getting BT to overlap it - which raises the question of why they spent about £3,500 per property that took it up on a solution that fails to meet the required spec!