Awful performance with CountyBroadband but fine with Vodafone UK

I have a 300mbps CountyBroadband fibre to the home connection. I have 3ms ping times to TeamViewer.com but using TeamViewer itself has become excruciatingly slow in the last few days.

If I switch to use my iPhone as a hotspot (via Vodafone UK) I get the normal responsiveness.

Is there any way I can see some sort of network performance statistics so I can narrow down the problem?

Clearly I need to go back to CountyBroadband to report the issue but I need some sort of network statistics I can show them as part of the problem report.