Geordie, I did have a very explanatory site about how the BBC iplayer 'assesses' vpns, but I've lost it!
Search on vpn and iplayer, and you'll find it.
It's not a BBC guy sitting there, it's about analysing the traffic from particular IP addresses. If a particular (vpn) IP address (or twenty), exhibits behaviour which persuades iplayer that it's looking at a vpn (contemporary hits, in the main) it blocks any IP.
This is very recent, and (being conspiratorial about this stuff) I find it difficult to believe this isn't down to upcoming EU legislation about freedom of access to digital media, and the absurd notion that the UK has already left the EU (which it hasn't, yet).
I would be delighted to throw £150 (the UK licence fee) towards the BBC so that I can watch their programmes - but I do not have the option of doing this. The BBC would be delighted to receive my £150, but they are not allowed to offer this to me. It's absurd. Some programmes, like Newsnight, do make much of their stuff available on YouTube, which is helpful (to me).
Filmon (fairly hefty subscription) makes live stuff available - but not the watch again options.
I'm mega pissed off with this.