Rafflesbear. That is The Rochester Seaplane / Aircraft Tunnels thank you very much. They look more like Train tunnels. From the out side.

They must have been the Canal tunnels Richard mentioned and the authorities just added features to them like adjoining tunnels and audits toilets etc. What a fascinating place to Explore.

Thanks Jim Carroll & Richard.
Indeed the most unlikely places do hide The most interesting places. When I used to guide Chislehurst Caves at the end of the day I would always make for the nearest pub for a pint or Six and has the years went by The locals gave me The Nick Name Caveman Pete. The Pub in question is the Bickley Arms.
The landlord told me once that The cellar of the Bickley Arms had Windows in it which immediately got my attention. Why would a pubs cellar well below ground level have windows. I asked The Landlord if I could view these features and he led me through the pub and down a stone staircase some 20ft in to the Brick-lined cellar. WoW and behold there in front of me was not one but two Victorian Box Sass windows.

Has I surveyed my surrounding I pointed out to the Landlord what I thought were at least two false walls indicating what was once a much larger cellar. On a return visit I went through one of the windows and found myself in a bricklined tunnel identical to the bricks of the cellar on the other side. I had borrowed three torches and a number of oil-lamps from the Chislehurst caves and with some friends who promised to await eagerly for my return pub side I ventured along this brick-lined tunnel some 2ft wide and 6ft high smothered in cobwebs.
Everyone back at the window was hollering and shouting after me and I shout back giving info to what lay ahead. Absolutely nothing but brick-lined passages. Then suddenly I found meself coming across a large square hole and the remains of what was once a shoot from the surface and I could see pinpoints of daylight shining in from what was the surface some 12ft above me. Pin holes of daylight to the left was clearly a bricked up door way again fashioned from the same brickwork has everywhere else. With no else else to go in any direction I went back the way I came and found meslf back at the windows with me friends awaiting there. I climbed back in to the cellar shut the window behind me and Said

I think I have just found my way into the coal and beer shoot of the former pub of this site The Tap.
The Tap was knocked down and the Bickley Arms constructed with the coming of the Railway to Chislehurst .

They simple built over the old cellar and constructed everything else above and around it by sealing up parts of the original huge cellar.I think the windows may have been installed so has to increase/ decrease ventilation in the new pub. Which was a pub but also a station Hotel. The Bickley Arms Hotel.