Give England to Italy. Drive everyone in England at gunpoint to live in a walled-off Westmorland to make room for the Italians who will move in to the rest of the country. Make it illegal for the so-called English to do anything but subsistence farming, and maybe some backbreaking manual labour outside of Westmorland for pitiful wages (and under constant watchful guard). And even then, make sure to murder a bunch of the English from time to time to remind them who's in charge and that they shouldn't get uppity towards their superiors.

And if any English complain, remind them that the Romans were living in and ruling England 2000 years ago, which obviously gives the modern Italians the right to inflict extreme disproportionate violence on any English who dare to complain about this arrangement.

i read a webcomic where that happens

unfortunately, they just put the cities in bathyspheres