After one week of a noisy phone line, coupled with frequent broadband disconnections, these problems were solved by Openreach replacing a corroded connector on the nearby telegraph pole. Since this was done (three days ago) my broadband speed has declined from around 15Mbps to 0.4Mbps. I understand that it is normal for speed to drop temporarily after such a repair, but to this extent? How long should it take for the speed to recover?
The exchange is in the next road and no further than the nearest green cabinet.
Fixed! Go to the fix.