I usually use corporate ethernet, public wifi or my home 1 Gbps virgin broadband with an asus router, pi etc .. so some options to assist in debugging.
i'm currently at a family members place and a) have no ethernet devices attached to router (nor my mac adapter), and the router is a BT HomeHub 5 which is limited in any kind of debugging/access. So I can't check pings from router, I can't try pings from thinkbroadband, I can't do a load test, setup QOS, do extra firewall debugging, look at vddl line stats, nor does the router respond via ICMP from internet.
I am seeing intermittent slow wifi behaviour on macOS + iPhone - perhaps down to 2 Mbps/0.5 Mbps, yet at other times it is around 60/16 (as expected). I get trouble on 2.4.Ghz & 5 Ghz and have done a full HH 5A router reset.
There are basically no other devices sending significant traffic.
I'm disturbed that pings to sites like bbc.co.uk are showing erratic response times -- 8 ms some of the time but frequent excursions into many 10s/100s
Perhaps the HH5A is rubbish at queuing? Perhaps it's overloaded? Maybe the vdsl connection is bad, maybe it is just wifi that is dodgy
Any suggestions before I contact the ISP (or return with more kit to test!)