It was good to see a different form of tunnel construction. In Dover we are used to the Napoleonic era construction method of hand hewn tunnels, and if the WWII pictures are typical then even the 1940s tunnels were constructed by hand, albeit with pneumatic drills rather than hand picks.
The Winchelsea, Westmount & Priory Hill Tunnel system seems to have been extended from the original quarry caves by using a boring machine, with the floor sections being cut in afterwards and blockwork arch sections being inserted at regular intervals.
I wonder at what point the extensions were constructed, assumption would lead us to believe it was in the period 1936-8 - then again, we all know what assumption is the mother of! Was the boring machine already on site, being used in the quarry - indeed was the quarry being worked during this period?
So many questions, and so little information seems to be available.