OK - that had been my assessment by flying over it, back in December, and deciding for myself exactly where it was … because my orbiting video showed it not to be where Google Earth (Litchi Mission Hub) was telling me it was.
Then - following @milkmanchris reminding me of MaritimeTraffic … I investigated further - and things are strange.
This is what Spitbank Fort looks like ….
(
me! 
)
On that you can clearly see the lighthouse, and you can clearly see the name that helps to orient the fort in the Google Earth (Litchi Mission Hub) images in a tic.
MaritimeTraffic has the lighthouse that’s on top of Spitbank Fort :
If there’s one thing that I know one can really trust in the UK- and that’s the positioning data provided by Trinity House of Lithghouses. So - that Lat./Long. will be correct!
The MaritimeTraffic “map” suggests that the lighthouse is on the south-west side of the fort.
Google Earth shows the correct orientation of the fort (I know - I’ve flown it!)
… and WP1 is the position using the coordinates from MaritimeTraffic (Trinity House) … again, showing it to be on the south-west side.
BUT … WP2 is where the red-and-white lighthouse is actually is located. (Refer to my pic above and the lettering for orientation.)
Those two positions are 26.8m (close to my 30 … considering I was 100m up when I did an accurate position recce) and, in Google Earth, you can also see a second “image” of the fort that’s a bit further to the east.
So - some things in Google Earth may be 30m (or more?) out … so, take care when flying real cosy Litchi flights. A recce flight higher/wider of any objects might be a good policy!
Note: That the MartimeTraffic map also suggests that the lighthouse is on the south-west of the fort would suggest that the underlying map data they use is also Google based.