What are the 'rainbow clouds' spotted over the UK?

A dog walker on the east coast near Whitley Bay, Northumberland, as rare Nacreous clouds form over the coastline. Credit: PA

Distinctive clouds have been spotted over UK skies in the last 24 hours.

The vivid iridescent high level clouds seem to display the colours of a rainbow - some likening it to a oil slick in the sky.

Having been mistaken for the Northern Lights (or Aurora Borealis) they have now been identified as nacreous clouds - also known as polar stratospheric and 'mother of pearl' clouds.

They are formed when the stratosphere becomes very cold - which is the case across the UK this week - probably enhanced by Storm Gertrude and Storm Henry in recent days.

The clouds are more likely to been seen in northern counties - but were seen as far south at north Norfolk this morning.

Their colour comes from ice crystals refracting the sun's rays to give a rainbow effect. They are usually spotted before dawn and just after sunset as their altitude catches the longest, late rays of sunlight.

Birds fly near Whitley Bay, Northumberland, beneath rare Nacreous clouds on the coastline. Credit: PA
The clouds over Edinburgh this morning Credit: @Mr_Mark_Brown
The clouds over Low Wood Bay in the Lake District Credit: Laura Scott