Mystery

Last night there was a patch of purple light in the very cloudy sky as I was walking the dog at around 6pm. It stayed for at least an hour, didn't move although at times some patches of low cloud floated over it.

It was too early for the moon - and in the wrong part of the sky anyway.

Anybody know what it is?

Another shot here - I've asked Sky at Night photo group if they can identify it. I bet the explanation is very dull.

(PS - SOOC after 8 second exposure - absolutely no enhancement but obviously this is a photo of a photo so the EXIF data is all wrong & I'm not displaying it).