This is fairly representative of what I usually get on a speedtest. This isn’t bad (in my opinion?) it’s just stability that is the issue. I turned on the " network performance graph" on Bf1 and (annoyingly) it didn’t find anything unusual, I sat in a server watching it until it inevitably booted me out again and there was no ping spikes, no packet loss etc. 
No firewall on, in fact, I never run any firewalls or anti virus ever (probably shouldn’t announce that…lol)
I can see the attenuator, seems to be on pretty tight, is there a way to check it for faults?
I’ll make a post on the Virgin Forums and report back, thanks 