The apps would be delisted in the UK app stores and will eventually stop working for existing users when not updated. That's also a security issue in itself.
For something like this you must start blocking at the network level, simply allowing the traffic would make these trivial to bypass via even something as simple as a web browser.
Which, unfortunately, is a rather risky situation considering for instance all the rogue ChatGPT-branded extensions and apps people downloaded without a second thought to their legitimacy.
We have been conditioned to view branding as the certificate of legitimacy, and that simply is not true for the Internet where branding can be copied and pasted in seconds.
The risk can be reduced with open source code, verified by the community. Usually when the "branding" gets too authoritarian, people reach for the FOSS version that seems the most trusted.
Stop using centralized software distribution systems. F-Droid, Debian etc are run by international communities, support Tor, and cannot be censored as long as we maintain access to the internet.
