"In the United Kingdom there are no laws forbidding photography of private property from a public place. Photography is not restricted on land if the landowner has given permission to be on the land or the photographer has legal right to access, for example Byways Open to All Traffic or a public right of way or an area of open access land. "
At the very least Temple Quay has an easement permitting a right of access. As long as you don't sit with a telephoto lens taking pictures through windows -- invading an individual's right to privacy or potentially coming under harassment law -- I think you should be fine (and frankly I'd like to see signs like this challenged).
[1] https://en.wikipedia.org/wiki/Photography_and_the_law#United...