I'd love your Download Speed and I'm paying BT for 20Mbps. I get 3.1 at the best but an Upload speed of .7Mbps.
Unless you're on their Virgin's Cable or Fibre Optic, you will be relying on BT's Cables between you and the Telephone Exchange.
Now it gets complex!
This is the Route that I am starting to follow: Get an ex-BT bod to check your internals (If BT come and check the House and find the fault is on your equipment, the Fee is horrendous) Then, you can get them to check your line etc.