Mystery caterpillar

Brian Statham swept these two caterpillars off Scabious on Bonsall Moor three days ago and we are both struggling to identify them. It looks like they are the same species,  it is not unusual to have green and brown forms of the same species.
Key clues to caterpillar identification are the month of the year and the food plant but neither lead to an obvious identification. Shaded Pug is one possibility but it does not appear to generally have the strong pale lines on the side and so far as we are aware has not been recorded in Derbyshire. I'll circulate the photos around some of the experts and see what comes up.
If Brian can keep them through pupation to emergence as the moth the mystery should be solved but that will be quite a wait.

mystery caterpillar