Jeremy, here is a more detailed map "ct-05-003a" showing the actual tunnels.
Could you tell if they seem accurate? I don't know the area.

p20 on
CFA2 Camden Town: Map book
PDF, 33.2MB, 58 pages
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/461187/Y11_VOL2_CFA02_WATERMARK.pdf
(https://www.gov.uk/government/publications/ses2-and-ap3-es-september-2015-volume-2-community-forum-area-reports-and-map-books)