Forward path equaliser arrived today - installed it and as intended it has reduced the downstream from 10-12 dBmV to around 6 dBmV without affecting the upstream.
Sadly this makes no difference. Speedtest.net to a Virgin test server still maxes out at about 30Mb. Pings are still showing lots of jitter with the max latency sometimes the top of the TBB BQM chart. Browsing seems to 'freeze' for periods and then unfreeze. Again this is wired (no wifi) and observed on two PCs and two Macs.
So whatever it is, the Forward path equaliser didn't cure it. Please open a case to resolve.