What caused this bizarre U-shaped cloud over King’s Lynn?

Did you see this mysterious vapour trail or cloud over King's Lynn yesterday?

At first, it looked like an aircraft had performed a U-turn over South Wootton around 4.30pm.

Except the radius of the turn was so tight it seems unlikely a plane could have performed it.

Could it perhaps have been a rare horseshoe vortex cloud?

The Cloud Appreciation Society's website says: 'This cloud forms in a region of rotating air, or vortex. Such vortices usually form vertically, sometimes leading to waterspouts or even tornados, but occasionally they can develop with a horizontal axis and give rise to a gently rotating crescent of cloud.'