Since some public-spirited residents of Coombe Lane cut down the dead and decaying trees which had been causing so many problems by rubbing the insulation off the phone lines, our broadband speed increased from around 2.2Mbps to around 3.4Mbps. Although this could also have been due (as Pete suggested) to a line upgrade from ADSL2 to ADSL2+, but we have had no notification from BT and I am not sure how one would find out.
Then, yesterday, we had an unusual visit from BT Openreach, asking if they could check out the appliances in our house as a possible source of interference to the broadband signal. I was out at the time so I only know what my wife told me. Apparently they went round the house checking for any appliances emitting interference in the 612 kHz frequency range - it turned out to be our Humax Freesat satellite receiver box (which has been on the blink for quite some time). How this could be causing problems to houses up the lane is still a great mystery to me as the box wasn't even connected to the internet or even anywhere close to a telephone cable.
Anyhow I have since found an article which provides a bit more information on the subject here. To any of our neighbours who may have been affected, we offer our sincere apologies - we had no idea. Hopefully it will lead to an improvement in your broadband signal - ours has already jumped to 4.2Mbps as a result.