Is it a Broom Moth?

Is it a Broom Moth?

Observation - Is it a Broom Moth?. Description: This large caterpillar (50mm) was found on tall grass during a bug hunt in a 3ft high wildflower meadow on chalk grassland on a hillfort in Sussex (Devil's Dyke). We then found a much smaller identical caterpillar about 14m away which was much closer to

This large caterpillar (50mm) was found on tall grass during a bug hunt in a 3ft high wildflower meadow on chalk grassland on a hillfort in Sussex (Devil's Dyke). We then found a much smaller identical caterpillar about 14m away which was much closer to a scrubby fenceline and grazed grassland. Dock and plantain were available close by