Floodgates

Technically the floodgates are still in situ at stations and in tunnels and still serviceable. However, AFAIK the gates are all secured 'OPEN' and cannot be closed. It is questionable whether, if they were closed, they could be opened again so easily. In most cases AFAIAA they are still proved in the signalling circuitry although I believe at one or two sites this may no longer be the case. Some of the floodgate relay rooms are hidden in the oddest places in tunnels and passageways and they have been left alone for the most part for the last 20 years or so ever since the Thames Flood Barrier was commissioned. AFAIK the Floodgate Control Room is extant but again it is questionable whether it retains control of all the floodgates because years of modernisation has led to some interruption to cabling which may or may not have been reinstated. Certainly most of the dedicated direct line Floodgate Telephones have been removed over the years, I recall removing those at Liverpool Street to make way for the new escalators.
At Old Street on the tunnel relining job a few years ago I disconnected and subsequently reinstated the main floodgate communications control cable which carried telephone and warning circuits to parts of the Northern, Central, District & East London lines but it was doubtful whether this was still a working cable!

Knowing LUL as I do I have no doubt that were it required for any reason the floodgates could be brought back into use but it would require quite a bit of work and a lot of money to repair/replace/update the equipment and meet current H&S and other requirements at all sites including the Floodgate Control Room.

I didn't think there was any floodgates on the Jubilee line? only the Bakerloo and these would be maintained by Metronet?

I was under the assumption that the floodgates were put in during WWII to protect the system from flood damage as a result of bombs. If that were the case then The Jubilee possibly hasn't got them, although I am happy to be corrected on this.

My understanding was that they were only at stations either end of a tunnel under The Thames, so presumably The Jubilee and Victoria wouldn't have them as they were constructed years later. Again, I would be happy to be corrected on this.

More were installed during the cold war, including on the Victoria Line.

I thought the Flood Gates were a WW2 thing?

The flood gates at Canning town being tested can be seen in a series of photos at andyharkness7058.fotopic.net/p7783010.html

Weren't there also side-hinged floodgates at stations in the lower circulating areas?

These are not floodgates they are watertight doors and they move very easy providing the floor is even, when I was on nights at Holborn I used to close them as the instructions in those days said they should be tested once a month.