After serious thinking Andy Burns wrote :
Planefinder.net does show a single aircraft arrive from the south, swizz
around for a bit (doesn't look like 40 circles on screen, but don't know what
resolution/interval it records at)

The centre of the tight circles was gradually drifting. It was too far
away to ID the type of aircraft, which had the setting sun behind it.
I've never seen one before with flashing white lights on the wing tips.