Alas, still can't get BBC iPlayer here..
I have the same issue, even if I use a UK connection, so I go into the settings to disable vpn with iplayer
If you resolve an IP to the ASN block that owns it you can tell (with reasonable accuracy) whether an IP is domestic or used for hosting, and similar to Netflix the BBC has started to routinely and aggressively block IP ranges associated with commercial hosting services. Combined with basic source IP monitoring (so you can see concentrations of connections coming from the same VPN exit nodes) it's quite simple to block VPN service providers.