NWSRG,
Get yourself over to BT SINet (
SINet) where you will find BT's official definition of the services they provide.
For example, broadband delivered under their "IPStream Max" product (
http://www.sinet.bt.com/386v3p1.pdf) , is defined as having acceptable download speeds between 288 and 8192 kbps (i.e. 0.2 - 8Mb).
Therefore, although frustrating, you may not actually have any leg to stand on when complaining due to their broad service definitions.