Thanks Liz for adding such an interesting and relevent comment. I was able to verify the existance of the Dorchester tunnel that you mentioned but sadly unable to find a good URL for the story.
Exactly one month before Hertford's tunnels were "discovered" by a local newspaper, The Guardian newspaper in the UK reported a story about secret tunnels under Paris, France. Apparently it was being used by a secret society - probably connected to the Skull and Bones.