What about YOU trying to pick up on the UK traffic, and getting your own redirect in first on your site. Admittedly, this is more advanced that a "little dabble", but it does avoid having to trust the affiliate program to properly tag your traffic through their redirect, which is probably not happening, especially given that the redirect is probably tracked to an affiliate subsidiary of the operator as a means of making a little money of UK players who find links to their site on the internet, but who they can't accept as players.
It would be better, and more honest, to simply show the UK traffic a page informing them that their country is not accepted. What they are doing could even backfire, as a UK visitor would see all the signs of a "scam site", having clicked on what they believed to be a legitimate online casino, only to end up on what looks like a site that just advertises a whole bunch of online casinos when they were expecting to find the casino they had read about or found in Google. This will lead to posts that describe the experience, which will influence people who CAN play at the casino into thinking it's not a real casino, but a "dirty tricks" campaign by some overly aggressive affiliate much like those fake casinos like "Real Vegas" that we have seen in spam and fake landing pages, only to end up with the Roxy Palace installer (among others, but certainly never "Real Vegas").