Re: "Not viable"
"Bear in mind that regardless of what service you use, there will be customers than a provider doesn't make money off of, and other whales that more than cover the lossy customers. BT could have easily been using the fat cat areas to fund those areas that were not "viable"."
I think that would be illegal for BT, or for any provider with a significant advantage in a competitive market.
If the customers in one town aren't profitable, serving them means making a loss - subsidising them from profitable business elsewhere. That means any new provider wanting to launch in that town couldn't possibly compete because the subsidy is anti-competitive. It's the first step towards creating a monopoly and is illegal.