Surely they'll not be shaping traffic for speed tests?
Dave, ideally you want your router as close to where the phone line comes in as possible, run a longer lan cable if required, it won't suffer as much and would have bandwidth to spare anyway.
Also try disconnecting any phone extensions around the house, sometimes they can act as an ariel and screw with DSL/ADSL.
Switch the router off, wait half a minute and switch back on try and force a resync with the exchange after doing anything with the cables.