When I brought my Cowberry plant to the Bramham meeting a couple of people pointed out that the leaves on one of the plant tips were spun together into a hibernaculum.
Today, I decided to have a look inside and, sure enough, a rather active, small, dark tortrix larva was revealed as the industrious occupant.
A text search of the UKMoths website leads me to believe that it is likely to either be Rhopobota ustomaculana or Olethreutes mygindiana. According to Sutton and Beaumont; the first species is said to be "Recorded among cowberry on the Pennine moors in vice counties 63 to 65 where it is locally fairly common." The latter is also described as "Locally common on the higher moors."
I will rear the larva through to the adult and, having just read the description in Jozef Razowski's Tortricidae of Europe I am expecting it to be Olethreutes mygindiana.