Alas, rural is pretty much anywhere outside a few city centers, and even in London there are parts where you can get stuck with an unstable 4 MBit/s DSL link (from personal experience).
I live in Bethnal Green (just down the road from "Tech City") and our entire apartment block can't get fibre, just a measly 4Mb/s. I don't know if BT is to blame, or the building itself, but it sure makes finding a flat to rent a bit of a lottery...