BBC iPlayer started blocking VPN users because it does not like the prospect of users all over the world accessing its premier UK service. It does not really track your true geographic location, but only checks your IP address to see if it is coming from a datacentre and not from an ISP. If it finds the former to be true, it shows you an error message and denies you access. On the other hand, if you use a UK residential VPN, there's no way BBC iPlayer is going to deny you access. This is because it cannot make out the fact that you are using a VPN. Your residential IP address checks out, and you can unblock BBC iPlayer.
