I don't understand the idea, the hole seems vastly too shallow to protect effectively from for example, bombing.
If someone carpet bombs every square inch of rural England then that would be the least of our problems.
It's... the very first line of the article
> When asked why he had lifted a section of a former plane into the ground in his back garden, Dave Billings shrugged his shoulders and said: "Why not?"
They have a YouTube channel, so I'm sure it is just as much for views as anything else.