craft1948 has it exactly ! I have had a BT line for 34 years, and I am also an ex-BT Engineer. When I phoned up this summer to ask why I was paying over £50 for line rental, unlimited calls (up to one hour) and broadband, they immediately halved that monthly bill to £25, incl VAT.
And I didn't have to kick up a fuss one little bit. I just wish I had done it a couple of years ago.
It pays to complain you know !
Its worth remembering that even if you are going to get everything from another telecoms company, you will almost certainly have to rent a line from BT. Talk talk, eg, provide NOTHING...ie everything still comes from good old BT, including the engineer who comes along to connect you up to Talk Talk.