I have just added this to the UK Map of places to fly your Drone at https://dronescene.co.uk
Easiest to reach from the trading estate near kingsnorth power station, try and park somewhere close to amazon warehouse. Caution when flying, keep an eye out for microlight aircraft from nearby very small airfield
Have got to try this, Did you have any trouble range wise, as it looks a fair way out. I have a Mavic pro so hopefully within range. Mark
I’ve made it from the grain road with the Mavic Pro once, but it’s quite a trek. If you get close to these co-ordinates 51°25’52.8"N 0°36’57.6"E it’s not far, a bit of a walk from the nearest vehicle access though. Starting from here will give you plenty of time at the submarine site. It can take a few minutes to locate the sub, so it’s worth taking a tablet with the location marked on google maps to use as a reference.
Hope this helps 
Next question, when is the best time of day? Being a landlubber I have no idea of tides. Thanks for the advise , much appreciated. As soon as the weather improves we will be heading down there.
This site gives you the tides at anytime of the year.
https://www.tidetimes.org.uk/chatham-lock-approaches-tide-times