Basement Mania in London
Very good article on the subject of digging deep basements in the Guardian. https://www.theguardian.com/money/2018/may/07/going-underground-the-subterranean-secrets-of-londons-super-rich?utm_source=esp&utm_medium=Email&utm_campaign=GU+Today+main+NEW+H+categories&utm_term=274068&subid=2272382&CMP=EMCNEWEML6619I2