I'm also Central London for work, I typically get at least 30/20 in the office without VPN, and at times up to 50/30, a lot less than the 80/80 I used to get 3-4 years ago in the same spot. With WireGuard I get consistently between 0 and ~10 down. I ran some tests with the guys in WireGuard IRC which seemed to confirm that the issue is specifically EE limiting UDP whether by QoS or otherwise.