I wasn't wrong and through the scope, short legs / all red bill were easy to see...
In the early sunlight and most of the views were sidelit or into the sun, despite the distance, what shone through (literally) was the translucence of primaries / secondaries - peculiar to Arctic Tern when ruling out Common!
But whatever the lighting, translucence shines through nicely, whether it's an under or upperwing view!
It was only in view for a few minutes once flying, showing a nice clean upperwing and then disappeared down the south end...
And I disappeared to check Whitemere and Colemere (nothing of note) and Wood Lane (just 1 Dunlin of note)