Jim, they   do/did exist. The regional control center in North Cheam was demolished in the 70's and a block of flats built on the site. My grandfather was told to get lost when he asked why the excavation was so deep during construction in the early 50s(He had been an engineer for the London Metropoltan Waterboard)
As bombs became larger excavations in clay offered little protection. Most if not all bunkers were inadaquate,including the deepbunkers on the northern line dating from ww2 and including Eisenhower's bunker at Googe street(or so the story goes)


https://www.subbrit.org.uk/sites/cheam-south-west-london-group-control/