Current line stats, O2 Wireless Box 2:
Uptime: 0 days, 11:14:01
DSL Type: G.992.5 annex A
Maximum Bandwidth (Up/Down) [kbps/kbps]: 1,200 / 9,587
Bandwidth (Up/Down) [kbps/kbps]: 1,191 / 6,487
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 19.0
Lne Attenuation (Up/Down) [dB]: 25.0 / 42.0
SN Margin (Up/Down) [dB]: 7.0 / 12.0
Vendor ID (Local/Remote): TMMB / BDCM
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 302 / 0
FEC Errors (Up/Down): 36 / 707,535
CRC Errors (Up/Down): 36 / 17
HEC Errors (Up/Down): 68,048 / 11
As you can see, it is currently synching at a 12dB margin. Last year it would sync at 10Mbs with a 6dB margin and rather lower errors (but it now seems pretty stable at 6.5Mbs).
I was wondering more about crosstalk between ADSL and VDSL in the copper cable from cabinet to here, which will now be carrying both types of signal in adjacent twisted pairs. It may also be that the cabling has been disturbed - I think they had some problems running the fibre to the next cabinet down the line which may run in the same duct at the bottom of the road.
As you say, for a 2.8km line 10Mb was quite a lot higher than expected, but something has caused to drop.