Inversion Layer?

Is this a temperature inversion layer? This is a view over the Cheshire Plain a few days ago, and I was struck by the strong line in the atmosphere... plenty of people were out walking but didn't seem to notice it. This was mid afternoon (I bet it would have looked glorious at sunrise!).

 

If you look carefully you can see Jodrell Bank (radio telescope) on the far right and the tops of the hills in the distance.

 

Thanks for looking!

Done