Oy, I had that same problem with my dsl connection, it had to run through the streets for about 2,5 clicks, that resulted in a max download speed of 800kbyte per second. The ping was good though, I had a better ping then I do now. Problems were when they fully opened my line, my computer tried downloading the files at around 1 mb per second and that made my line disconnecting and connecting over and over again, at a certain point that was a few times per minute. They finally downgraded my line so it could only download at 800kbyte a second max, that solved the disconnecting and reconnecting. At a line measure, they discovered I was just in the marge of what db my line should get, hearing your complaint, I think you aren't in the margin of what it should be, although I doubt BT will give a rats ass about margins. Could be that the quality of your line is crap and should be replaced.
My solution at the time was going over to cable, that results in a 5 megabyte per second download speed, a 3megabit upload, a 80 mbit download and 5 mbit up in octobre and costing me around 64,95 euros per month. It's not cheap, but I get da bomb diggy diggy bomb download speed with it
Solution for you: flee your country
or bomb BT ( probably won't help you, but it'll ease your pain
)