Pillar & stall chalk mine.
Was re-used as a Regional Seat of Government underground bunker during the cold war. Now used commercially for storage.
References
“Caves & Tunnels in SE England Part 5”, Chelsea Speleological Society page 54-56
References
“Caves & Tunnels in SE England Part 6”, Chelsea Speleological Society page 46
“Caves & Tunnels in SE England Part 8”, Chelsea Speleological Society page 16-18