I have a BT line, paying rental to them, but use another ISP. I am with a Level 1 exchange and don't believe there will be any increase in speeds any time soon. Outgoing calls are diverted via my ISP call package that gives anytime 500 free minutes to regular land lines and for anything else I use VoIP. As a rule my down speed is around 6.8Mbps, so all in all there seems no merit in looking for alternative suppliers.
Not the way BT sees it though, with promises of blistering download speeds for a rental that is next to nothing judging by their WEEKLY mail drop to me plus a couple of emails or so weekly and enthusiastic advertising for their broadband service in a leaflet that comes with their quarterly account. All wasted on me because there really is nothing better available for me; in fact it would cost me much more, in the term, if I did to switch to BT.
It seems to me that many other Internet user are in the same position as myself so just a suggestion to BT [got your hearing aid in?]. Cut out all this unnecessary advertising and invest the money instead in actually improving the infrastructure in rural areas. Then, and only then, might we actually consider your services.