That word would be castle.
The Merriam-Webster online dictionary defines castle thusly:
castle: a large building usually with high, thick walls and towers that was built in the past to protect against attack.
You will see, then, that the building that this Englishman took refuge in - - his home - - wasn't also his castle, because it offered him no defense when he was attacked.
Of course, even in feudal days, a castle by itself wasn't secure; it had to have armed defenders. And that is where UK has failed its