Ok thank you
That saved me £12
I do have another extension installed by sky, as its no longer needed I removed it which gave me 1db back
The house has sockets all over the place, I haven't tested them yet but I removed the daisy chain onward extension cabling at the socket where the adsl will be, whether this makes any difference, I think it gave me consistently .5db back.
All sockets have ring wire removed and insulated.