You say you're using the the Unifi Wifi AP's, but what router are you using? If the the x6 speeds is ok-ish and x1 isn't, then this is a contention problem.
The root cause here is that Origin haven't bought enough bandwidth from either BTWholesale or TalkTalk Business or haven't got enough bandwidth to their upstream transit providers (former is much more likely as latter should mean they're on LINX and that part is very cheap compared to wholesale bandwidth). You can't do anything about that short of switching ISPs and whinging loudly, though.
However, if you have OpenWRT, Asus, Ubiquiti router (anything better than the USG 3P or the EdgeRouter Lite), pfSense or other Linux router, they should have fq_codel since it's in the kernel now (often just exposed as 'smart queues' in config screens). It's not a magic bullet that will solve all issues, but it will help you use every last bit of bandwidth you do get as efficiently as possible in the meantime.
Thanks for the reply. Yes I think it is backhaul - kind of wish they would just tell me and say leave if your don't like it. Rather than getting me to do Speedtests all times of the night to keep me busy,,,
Router wise I have a tp-link mr6400 currently - i changed a couple of months ago after I had problems (whole other story

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EDIT'd for clarity and this router has a 4G sim slot so I could carry on having internet while they all sorted themselves out. I do have an Archer D5 as well and a Asus DSL-N16 - that was given to me by Origin that I never used.. Any of those do it?
This morning test
Edited by bounderboy (Wed 22-Apr-20 17:22:49)