Thank you NewForester.

Had taken numbers from the HomeHub and BT's IP Profile and calculated that my line would get 12.5 to 14Mbps into which BT's estimate of 13 meg fitted bang in the mid-range.

BT's revised estimates (which are without any coherence) have been re-cast to 50% of the possible data throughput - and they themselves cannot get the relevant BT team to provide any explanation.

For Honor Oak - I would guess you are on Forest Hill exchange - but that can be tested from BT's web-site by typing in your landline number.