Silbury Hill 180
Image by Moth

Of course they are new tunnels, if the old infill material was all that was being removed they would remain the 1849 and Atkinson tunnels. This is a rebore that will take 10" off the walls. The walls will be of totally never before seen archaeology - it a new tunnel !

VBB

No I think it is rather an expanded Old tunnel at best a 10" tube around the old tunnel.
They are not starting a New tunnel from scratch.
I'm looking forward to it all happening and hope you share your photos when you go inside for a poke around.