I don't think BT charges ISPs for a remote diagnosis line check. Oldbeefer is 100% correct on the benefits of using the main socket. I suggested to a mod on this site that he moved his router from upstairs to the primary socket in the hallway. His speed jumped from 600k to 6Mb after a couple of days having allowed the kit in the exchange to re-set itself to adapt to the improved wiring.
Rans6Andrew, that sort of distance to the exchange is probably in a straight line which suggests you are close to the edge of the exchange area and hence you will have a far slower speed. The further the distance over copper, the slower the speed. That's the laws of physics I'm afraid. Your service provider may have access to BT's fibre to the nearest cabinet which would give you a far higher speed. If you buy a fibre based service from BT then they will give you a couple of sports TV channels for no additional charge.