Well, the DSL saga continues. The call has been escalated by my ISP to BT, and BT have called me for details.
This evening, I ran a fresh connection for the DSL modem from the back of the master socket. The downstream noise margin has gone from 5 to 10, and the ATM sync rate has picked up a good megabit or so. Unfortunately, this hasn’t translated in to an increase in IP speed – in fact, my speed tests through my ISP portal are showing 500 kbit, not 5000 kbit 🙁 🙁 🙁
Hopefully the system will reset itself over the next few days and my speeds will re-balance. The fact that my DSL picked up signal strength when I put in a dedicated path from the master socket means I also have a fault somewhere in my wiring. I might well re-wire using cat5 cabling – the only issue is getting the cable up to the computer closet.