Balls...

On the info page:

https://www.johnlewisbroadband.com/faq/#whymanage

we learn that on the "up to" 38Mbps service the only things that you are allowed to use AT that speed are Web browsing, Email, and "John Lewis Broadband FTP" (whatever that is). Gaming is apparently "Prioritised" at 2Mbps.

John Lewis have clearly been reading the official ISP bullsh!t manual before setting up this system.