That's because London is on clay. The Reading guy was mostly on chalk (and was himself an engineer). It sounds like the water table was a long way down as well. Soft clay or waterlogged sand are more like digging a hole in a bowl of custard. There are a lot of things that can go wrong - in the case of clay, even if you don't collapse the hole the clay can expand for years afterwards ("heave").

Doing underground expansion correctly won’t cause streets to sink.

The title is "not even" clickbait, just very confusing.

"The unique complex contains more than 1,300 square feet of underground space, including tunnels and storage rooms - and even a hand-built railway."

(Edit: I mean the original article, not the submission)

sorry for the capital M … I have fixed in the title to 15m as in metres

that’s ~ 45 ft underground, I believe … perhaps not that impressive, but quite funny since I would hesitate to undermine my own house and surely this makes it worth less

> Curious how he got planning permission. Or if he got planning permission.

The answer lies in your first sentence:

> 300k in Tilehurst for a house with a pool is incredibly cheap.

My hunch: Sound-deadening baffles.

Is that an issue in the UK?

>1,300 square feet of underground space, including tunnels and storage rooms - and even a hand-built railway.

Says it’s vacant. Says guy started in the 80s. Going to deduce he is/was older and moving on for any number of normal reasons. Why is the reason so important?

Looking at the pictures, my best guess is that the maintenance has been an issue for some time.

I don’t think it extends beyond property limits.