The idea of quarantining (effectively putting everyone under house arrest) an entire country. The legal issues which could arise are mind-boggling
Article 5 of the European Convention on human rights does allow this in principle as long as prescribed by law (and presumably necessary and proportionate). But that’s just the start of it 
It basically puts the state in charge of the detention of tens of millions of people. People have rights in detention. How could a state effectively administer this? It couldn’t. No way.
The state would be responsible for the health and well-being of the entire country - delivering food if it wasn’t a available eg by supermarket delivery (but who would deliver?) and making sure the system was in place to do so
The state would have to ensure that the electricity network, heat, gas etc kept operating. Who would do this? Special dispensation for those industries? Who would monitor them for disease control?
Then there is policing the quarantine itself. It would have to be the police and army. What would they do if someone broke it? If there were eg food riots? What lawful force could they use? Would have to be proportionate to threat posed by millions of non-infectious people
The state would have to put in place a system of authorisation for emergency travel eg for medical and other reasons. How would it administer for such a large group? No way it could
Nb the 2020 Corona virus regulations would not allow this kind of approach As far as I can tell - limited to people reasonably suspected of having the virus or having travelled from particular countries legislation.gov.uk/uksi/2020/129/…
Would have to provide eventually for education of children though I imagine a short break wouldn’t be a legal issue
The govt does have powers in theory to restrict movement of/detain an undefined class of people but the restriction would have to be proportionate to the (obviously legitimate) end of protecting public health legislation.gov.uk/ukpga/1984/22/…
If people were treated unlawfully in detention the state must give access to an effective legal remedy but if all the courts are shut or severely limited then this would be impossible. Indeed, for 60m people it would be impossible anyway
I wouldn’t usually speculate on a doomsday scenario like this but since it’s happening right now in Italy it’s a real thing which could be happening in U.K. very soon. I’m sure the government lawyers are boggling their own minds right now
Have heard conflicting things about the Italian rules but this sounds pretty severe (and hugely open to misinterpretation)
