|>>|| No. 2230
It doesn't have to be through BT. An independent BT subsidiary called Openreach installs and maintains the physical equipment. Openreach are legally obliged to provide services to all companies at the same price. Openreach charge £38.41 ex vat to connect a land line, so BT are really taking the piss with their connection charge.
Sky are probably the least-worst of the major providers, but they're not a patch on specialists like Zen, Pulse8 or AAISP. Before you choose, check that you'll be able to get fibre, otherwise you'll be stuck on "up to 17MB/s" ADSL. Virgin Media are worth considering if you can't get Openreach Fibre; their service is somewhat unreliable, but very fast.