What is it with Brits and digging tunnelsystems underneath their houses? William Lyttle ("The Mole Man of Hackney"), "I'm just a man who loves to dig".
My grandfather had a kind of similar situation in Genk, Belgium where he bought a house and discovered a whole basement system that spanned a good part of the neighborhood.
In my teens I had enjoyed a book series "Tunnels" by Roderick Gordon & Brian Williams. The story cranks the mole fantasy up to 12 & surprise, surprise... it is set in some london downtown.
My grandfather had a kind of similar situation in Genk, Belgium where he bought a house and discovered a whole basement system that spanned a good part of the neighborhood.