The flights are relevant to whether or not lockdown works, and how bad any second wave might be
I don't think so. This is a global issue and I suspect virtually everyone who arrives has been in a country with some degree of lockdown anyway and once they arrive here, they also have to go into lockdown. OK they might go to a supermarket but if you have symptoms you are supposed to stay at home and if you have been locked down elsewhere you shouldn't have symptoms or even be infected.
And the numbers trickling in are tiny.
Once lockdown is eased here and elsewhere we might need more stringent controls, but at the moment I don't think it's an issue at all.
As for the A&E thing I suggested on this or another thread that you could go to A&E and get someone else from another household to go in for you to get help, so you weren't just walking into A&E with covid. Some hospitals may have a signposted area for covid patients anyway so you wouldn't necessarily even need to go near normal A&E. But if I think I might die, I'm not waiting for an unqualified call centre person to decide if I have the chance to live or not. Hopefully I will never find myself in the situation.