Have you tried turning it off and on again?

the cable you may have seen being put in from Norwich to Aylsham a few years ago was actually Virgin Media to feed the new estates
PS my little bit of North Norfolk has FTTP and wonderful it is too 150 down instead of 3!!!

Norfolk is largely an enclave of Market A (ie BT-only) exchanges too, making it difficult for altnets to run leased lines and buy bandwidth as the prices on monopoly exchanges are sky high. While there's mediocre coverage of FTTC in larger villages and market towns, there are 2 problems:

1) quite a large number of people live in periphery of towns and villages and they're lucky to even get USO speeds.

2) Even if you have FTTC in Norfolk, there's a serious problem with capacity - the backhaul is all too easily overwhelmed and congested.

making it difficult for altnets to run leased lines and buy bandwidth as the prices on monopoly exchanges are sky high

If I am understanding you correctly I think you have this backwards.

The reason consumer wholesale prices are high on market A exchanges is to give altnets a better return on investment if they were to come to the area to install their own network. BT are not allowed to compete with them using their lower prices and so the altnet are not having to price as low to get customers. The prices are specifically high to allow altnets into the area not to block them.

The cost of leased lines and core bandwidth is nothing to do with market A.

Two points.

First, ian72 is correct. Ofcom classify exchanges as Market A because there is no LLU presence in them. Not the other way round. LLU means that such ISPs have installed their own MSAN/DSLAM in the exchange. Whether or not they do that is a commercial decision they make, unless of course the exchange is so small there is no space for that.

Second, I assume you mean BT Wholesale, which means a hundred or so ISPs can supply. Not just BT Retail and BT Business. Even Sky and TalkTalk could through BT Wholesale. They just choose not to.

AIUI there are a tiny few exchanges in the north of Scotland that only have BT ISP. They were paid to set them up, and did so on condition that they could have exclusive rights.