I have an almost identical graph:
http://www.thinkbroadband.com/ping/share/a3c2384d89c...
This is on ADSL2+ on WW FOWE.
I'm loathe to raise a ticket because it's not affecting me too badly and my line might be reset as part of any diagnostic procedure, which I don't want.
I'm somewhere in the same area code as you, and while I don't have the massive jumps in latency in the evenings, I do have a rather rough looking graph 24/7, and non-zero packet loss in the evenings:
http://www.thinkbroadband.com/ping/share/512bd86e877... (FTTC in my case).
Plus the single threaded issues generally, of course (except when the combination of bng1 and good backhaul align correctly)
Zen are already well aware of my problem, though
Edited by deleted (Fri 18-Mar-16 14:44:21)