Except that your "fake news" that they don't is in fact the fake news, because Three have information about it on the web site, in the terms and conditions and even gave it a name and called it "Traffic Sense".Just so you don't feel singled out, I'm on Three and see exactly the same result when I use a VPN during periods of high contention when I see 56k modem levels of slowdown.
What with the "fake news" of modern times being the norm, three don't admit to using traffic management either.
"TrafficSense™ is a term we use to describe how we manage traffic on our network. Whenever we do this, it’s to provide the best possible internet experience for all our customers."
They are clear that to ease congestion they will traffic manage.