Under UK regulations, it does not matter whether marketing is "targeted to selected potential customers" or presented to UK citizens at large. What matters is the content of the marketing, and whether or not it complies with the rules regarding advertising.
Naturally, where sister sites get involved in cross marketing, affiliates are going to raise objections about losing out because they are being bypassed, and have no real means to check whether or not "their" players originally introduced to the group are being tagged to the original referrer when they respond directly to a cross marketing invitation. This has become a particular concern after some programmes were caught deliberately trying to shift players an affiliate brought in from the initial site to a sister site as a means to cut the affiliate off from receiving the ongoing revenue share.
Infamously, Grand Prive got caught red handed when they directly emailed their players with an offer for a new casino Villa Fortuna, and then got all hot under the collar when someone posted about this new casino and the email they had received on the forum. The member was asked to remove their post because it was a "secret" that this new casino was being opened, but it was too late, the cat was out of the bag and affiliates witnessed the start of the process whereby they were about to get royally screwed by Grand Prive. Affiliates were also being lied to as they were told that the original 5 Grand Prive casinos were to be closed, which was a cover story to explain away a sudden fall in revnue share income from players they had referred. In fact, these casinos were not being closed, affiliates were merely being detagged on the sly. In the end, Grand Prive announced that they were simply closing down the affiliate program, and they would no longer get paid as promised for any future activity from the players they had brought.
The damage this did to the integrity of the industry is still being felt, and every time something happens that appears to be designed to disconnect players from their referring affiliate, you can expect affiliates to start asking questions, often with the view that the programme needs to prove they are innocent, rather than having to be caught red handed by affiliates scouring their data.
UK self exclusion rules are a mess, but any casino operator that uses a complex relationship structure is leaving itself open to breaking UK SE regulations, and in particular open to the SE scammers who are taking advantage of this mess by being smarter operators than the casino, and then using the SE regulations in a "cherry picking" manner by exercising their legal right to a refund of deposits when they lose due to being able to demonstrate they have self excluded at a "sister site", whereas operators with a complex sister site structure are prone to not cross checking for self exclusion and thus ending up paying such scammers when they win, who of course then keep quiet about their SE. The underlying "tool" the scammers are relying on is that by the regulations a casino that takes bets from a self excluded player from another sister site must void all the bets and return the players' funds. Having V&J and Cassava as sister sites effectively means that if a player self excludes from V&J, they should also be self excluded from all related sites, including the vast empire of 888 sites. Given how badly 888 operate their cross referencing, often only picking things up when a player wins, the SE scammers could have a field day by using SE at V&J, and then playing at the 888 sites, taking no bonuses (which is the main reason 888 sites even bother to run a sister site audit on a new player's withdrawal), withdrawing wins, leaving it a bit, and then claiming that they had SE'd from V&J in order to force the other 888 sites to return their deposits under UK regulations. Strictly speaking, the winnings from the other 888 sites should also be returned, but the money is already with the scammers, leaving 888 having to take them to court to recover the incorrectly paid winnings.
This mess will continue, along with the scammers, until the UKGC bring in the central SE database regulation, giving operators a single database on which to record SE requests, and also check their new players against for SE elsewhere in the UK regulated industry. This should also have the benefit of shutting down the SE scammers.
The CMA are now investigating the industry, at the request of the UKGC, as it is believed that violations of UK law are widespread. This is probably because the UK facing operators are still relying heavily on what they have always regarded as "standard industry practice", but this is the first time they have been licenced by a country that actually lets it's own citizens play, hence the clash between the industry and one country's domestic laws.
Whilst many UK facing operators hold primary licences in Malta and Gibraltar, the difference is that the Malta licence forbids citizens of Malta to be accepted as players, and it's similar with Gibraltar.
Operators need to keep a close eye on how the CMA investigation develops, and should also be looking at the ASA rulings being made against complaints made about specific marketing shots from online gambling companies. Leaning from mistakes made by the competition, rather than learning from your own clashes with the ASA, is a wise strategy to follow.
There is also likely to be an increase in UK players using the courts to resolve issues, particularly where SE is involved, as it has emerged that the UKGC is so overwhelmed that it has resorted to telling players "take it to court", and of course the ADR system is not permitted to mediate on SE cases, these must be referred to the UKGC.