Nacreous cloud

I think that this phenomenon, seen whilst walking the old collieries on Combs Moss, is Nacreous cloud.

Nacreous clouds are wave clouds. Their sheet-like forms slowly undulate and stretch as the waves evolve. The clouds can also be associated with very high surface winds which may indicate the presence of, or induce, winds and waves in the stratosphere. They form at temperatures of around minus 85ºC, colder than average lower stratophere temperatures, and are comprised of ice particles ~10µm across. The clouds must be composed of similar sized crystals to produce the characteristic bright iridescent colours by diffraction and interference.