At the present the main site in question is the BBC. I cannot remember exactly when but the law was changed about 12 - 18 months ago to make it mandatory to have a TV licence to watch the BBC iPlayer, at least you have to click a button saying 'Yes, I have a licence'. Then about six months ago they added software to the iPlayer to block VPNs.
This is ironic because the biggest users of iPlayer via VPNs were ex-pats who were trying to watch some UK TV from foreign parts, using VPNs to get round the geoblocking features of iPlayer. Ironic because there have been surveys showing that many of these ex-pats would cheerfully pay a subscription to watch iPlayer.
As far as I know, the BBC is at present the only site doing this.