This isn't true. I work in the UK ISP industry, and the reality of the UK world is you have basically got two access options :-
1.) You access via a copper line (a traditional phoneline). Phonelines are owned by BT Openreach, who run the infrastructure, and who are forced by the regulator to lease the lines to ISP's.
a.) If you live in a rather densely populated part of the country, you will have access to multiple LLU (local loop unbundled) providers. These are ISP's who have put equipment in the old BT exchanges (Central Offices in US telco speak). The provider then handles your internet from that point on.
b.) If you live in a less dense population area, you will not have that option. You will instead get your data via an ISP who BT Wholesale access to the internet from. Multiple options exist for these ISP's, but BT charge a lot more for this service than it costs an LLU provider to deliver. Of course LLU has startup costs that Wholesale doesn't, but generally you get a worse service in Wholesale land.
c.) BT Openreach are starting a FTTC (Fibre to the Cabinet) deployment, which is putting VDSL capable DSLAM's in the little green boxes you find on the streets. This gives a much shorter DSL line. BT Openreach are either providing this as a wholesale service, or they are providing an ethernet handoff to an LLU provider in the exchange. Either way, no provider is "unbundling" individual cabs yet, and the customer numbers and economics make it very unlikely that will ever make sense.
2.) Virgin Media Cable.
Realistically, the UK only has one cable provider, and that is Virgin Media.
Most LLU providers sell an effectively unlimted broadband service. Sky do for Â£7.50 if you are taking another Sky service, and the other LLU providers have a hardly enforced fair use policy.
This isn't so true on the Wholesale services. Most have caps, or traffic management, or some other impact on your service. The economics of the wholesale deal basically mean an ISP would lose money on every broadband customer if it didn't do this, or would have to charge prices so high the market wouldn't really bare it. Remember while people that read slashdot care a lot about internet connections, most people don't. Some more geek friendly ISP's, like A&A exist, who provide a pretty good "straight dope" on what they are doing with your connection.
Virgin have a constantly changing traffic management policy, but generally packetshape hard in peak hours on the cheaper packages, but have very little traffic shaping out of peak hours, or on the more expensive and faster services.
Finally, remember BT aren't JUST a infrastructure company. They have BT Retail and BT Buisness arms as well, which will actually sell you a DSL line or whatever. They buy this from BT Openreach or BT Wholesale just like other providers (at least in theory - the industry doesn't think the Chinese walls between the parts are that tight).
The reality of the UK Internet, is it doesn't have the headline speeds of places like Sweden or South Korea, but almost everyone (not quite, but close) gets at least some form of broadband. Unless you live in the middle of literal nowhere, you most likely at least have some form of ADSL.