My 2862n which had been running without issue for years @ 13Mbs/1.0Mbs started running @ 180kbs/240kbs, yes slower down to up!. My ISP is Plusnet. I've not changed anything. Each reboot gives ~same up speed but different down, but always slower down to up. SNR=6, ATTN=52. Running on latest firmware. Any ideas what problem could be, is it the 2862n?

Could be an issue on your line. I'd contact Plusnet in the first place and ask them to investigate (run the GEA report on your line).

Thanks for the suggestion. Before talking to Plusnet I thought I should eliminate as many problems my end as I can. First is to try a different RJ11 cable from the BT Master socket to the 2862n, for this I need to get a new RJ11 cable. If this gives the same result to then try the same cable to my "spare" Fritz!Box router, if this gives the same result I'll have eliminated everything my end so then it has to be Plusnet.

Well, if you want to try to eliminate as many things as you can, you should also try a different filter, and above all things, plug your router to the master socket (test socket slot).

I'd try to get Plusnet's help at the same time. It's not like you have to eliminate everything at your end first; you can do things simultaneously. Especially that you don't want to produce more e-waste by ordering more RJ11 cables.

More specifically, Plusnet can run a GEA test on your line and it may pick up something on Openreach's network.