VPN wouldn't work. Whatsapp is tied to a mobile number so they would just blacklist all +44 numbers. No matter where you are, even if your an expat, it won't work....
Meta has multiple server relay nodes in EU. Just shutfown the relay nodes in UK and geolocation block all incoming connections to EU servers coming from UK IP address. The phone number is just at user registration. Back-end they know. Heck, my whatsapp even route my voice call info (likely they transcribe and send to FB adverts processing via chatGPT-like solution) and flooded my FB with related ads derived from my voice call keywords.
If they really don't want to serve the UK market, then they can block +44 but given the prevalence of WhatsApp in UK and rest of the world(except for the US), I can see how people can start shipping EU SIMs to UK for WhatsApp use or create SIM SMS relay service with foreign numbers.
What if I enter +44 118 999 88199 9119 725 3 as my phone number?
This instantly puts me off WhatsApp from a reliability perspective. Your identity needs to be decoupled from something someone else controls.
I don't care what Meta does they are big enough to solve the issue.
I was talking about smaller messaging apps that can't just refuse to comply.