Possibly the best rebuff to all the arguments in favour of privatisation. (Oh, wait, it has been pointed out to me by StrawberryFrog that the railways are probably up there too. My mistake.)
Like other companies with 'British' in the title (British Airways, British Rail, British Gas etc), British Telecom started off as a nationalised, or state-owned, company with a monopoly. However, with the New Right of Margaret Thatcher and John Major, nationalised industry was declared a Very Bad Thing and privatisation commenced.
It was argued that this would increase competition resulting in level playing fields, lower prices, higher quality services blah blah blah. Removal of monopoly = competition = good.
For some bizarre reason, though, British Telecom was allowed to keep its monopoly, sort of, maybe. Something to do with it owning the physical means through which telephone calls are transmitted. I'm not sure. But the point is, BT appears to be the only privatised company which has managed to hang on to its monopoly (yes, I know other companies exist, but a free market it is not), with resulting high prices, as the competition is laughable.