It turns out that the terrible speeds weren't due to the internal wiring or router.
BT Infinity has been ordered and a new BT phone line was requested at the same time. The new number is now active (Infinity has been delayed until Wednesday because of capacity issues) and the Sky ADSL is still connecting; the downstream sync has somehow increased from 4.5Mbps to 19.8Mbps and my pings have stabilised.
It turned out that we had Sky as a voice/ISP but the line was still being rented from BT, so I'm not sure why this has happened as I presume they wouldn't have physically changed anything at the exchange when 'turning on' the new line. Oh well, I'm not complaining.
Going back to Infinity, does the revised activation date seem optimistic? BT has told me that the engineer went to do the work on Friday but found there wasn't any capacity; Openreach would have to be pretty on it to have the work done within three working days. Is there any way to check whether this is actually the plan or if BT has just given me a place holder date that will slip? I'm on Vauxhall cabinet 25.
Edited by Damarr (Sat 23-Jul-16 14:11:16)