No interactions present.
....where it is though on nettle as this is the foodplant.
The BugGuide website (http://bugguide.net/node/view/311623/bgimage) has a very similar image with the note; "Much less colorful than it was, with most of the red gone except for the prolegs. It's still a light and unusual color for a Red Admiral caterpillar."
I shall add my agreement to your tentative identification.
Lat/Lng: 50.64509, -2.46877
OS grid ref: SY669829