If it came to it, Whatsapp could be blocked at the network level. All the gov need to do is impose regulations that forbid ISPs and other infrastructure hosts to carry the traffic.
Now you need to block VPNs, and the cat-and-mouse game gets in full action!
Also, at this point you've basically implemented the roots of a British version of The Great Firewall.
> such regional restrictions are easily bypassed and WhatsApp is popular enough to make people try it. So that would then normalise the practices such as side loading / jail breaking and avoiding regional restrictions.
If people would be doing this (using a VPN, for instance), they would know how to bypass those restrictions.
Breaking encryption is not good for anyone and won't solve absolutely any problems, except the "problem" of right to privacy.