A democratically elected government can't (at least not if it wants to remain in power) breach the UN convention on human rights, imigration isnt an invasion (and thinking it is is another indicator of how authoritarian minded you are) , but even in war torpedoing ships full of unarmed cvillians and then machine gunning them in the water would be a war crime.
If David Cameron for example tried to order such a policy it would never get through parliment - and even if it did the Queen could still order the armed forces not to obey (which would cause the government to fall) - and if by some fluke such a policy was carried out the government concerned would become an international pariah (which would also cause them to fall)
I can never decide whether you are joking, trolling, or if you are serious - if its genuinely the latter you ought to seek help for your sociopathic personality disorder
from the UN declaration on human rights
from here
http://www.un.org/en/sections/what-we-do/protect-human-rights/index.html