OK I've reset the modem this morning and it looks like DLM intervention is removed (both Inp % delay are now 0)
Still on 7.64Mbps according to BT Performance test though.
Can you explain why the downstream snr is so high, I thought it should be 6dB or thereabouts?

STATS

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BusyBox v1.9.1 (2014-01-21 16:44:38 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

# xdslcmd info --show
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 1128 Kbps, Downstream rate = 14104 Kbps
Bearer: 0, Upstream rate = 797 Kbps, Downstream rate = 7895 Kbps

Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 13.5 15.8
Attn(dB): 32.6 0.0
Pwr(dBm): 10.2 10.5
VDSL2 framing
Bearer 0
MSGc: 87 26
B: 236 31
M: 1 1
T: 21 34
R: 16 0
S: 0.9549 1.2427
L: 2128 206
D: 1 1
I: 254 32
N: 254 32
Counters
Bearer 0
OHF: 14240 20355
OHFErr: 2 0
RS: 892953 691870
RSCorr: 3 0
RSUnCorr: 7 0

Bearer 0
HEC: 6 0
OCD: 2 0
LCD: 2 0
Total Cells: 3257359 0
Data Cells: 465906 0
Drop Cells: 0
Bit Errors: 0 0

ES: 2 0
SES: 0 0
UAS: 23 23
AS: 216

Bearer 0
INP: 0.00 0.00
INPRein: 0.00 0.00
delay: 0 0
PER: 15.09 10.60
OR: 49.27 24.14
AgR: 7944.77 820.79

Bitswap: 155/155 0/0

#
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Your speed has been capped by DLM to force your SNR to rise.

Also, you're on a faster broadband profile giving you an upstream sync of 797.

That's what I was afraid of, used to get this on the dreaded adslmax. I presume it's no longer possible to ask for a snr reset now it's FTTC?

The usual reason for DLM capping is because of a line fault. You really need the fault fixed.

The trouble with this conjecture is that, if your line is now working well, your speed would, by definition, be at the very top of the bands or a few bits below. However, your downstream speed doesn't match with one of the bands published by Plusnet:
http://community.plus.net/library/browsing/fttc-dlm-...

Upstream certainly has a band with a top speed of 0.8Mbps, but downstream has bands for 1.5-3.1 and 7.5-15; nothing that has a top speed of 7.9Mbps.

However, that list of bands looks suspicious around those speeds: every other band overlaps with the ones either side - yet no band exists involving speeds 3-1 - 7.5. Perhaps there are some missing

You are right that it is impossible to ask for a DLM reset, and impossible for an ISP to order it. Openreach are in control, and require that the only time a DLM reset can be requested is by an Openreach engineer that has fixed a line fault.

Under normal circumstances, DLM would get around to de-intervention if the ES value stayed low for a good long period. However, the word is that BT have turned off the intelligence behind DLM (while waiting for a court judgement on a patent), so it no longer monitors your line. You may be stuck for a while...