In December 2011 there were a number of lenticular clouds spotted in West Yorkshire. This is a rare occurrence in the UK as there are no areas particularly high enough to cause an obstruction to the air flow. These wave clouds were in fact caused due to stable, moist air that travelled across the Pennines.
Unfortunately there is not a great deal of information about this lenticular cloud, however, there’s some nice photos.
This has made me curious about other altocumulus lenticularis that have formed in the UK, but examples of this are proving to be hard to find.