Cinnabar Moth (Tyria jacobaeae)
The Cinnabar moth is a member of the Tiger moth family that flies late at night but you do see them during the day as they are easily disturbed. They fly from late May until July and the caterpillars will appear on Ragwort in August.
Ragwort is a plant poisonous to animals and the insect takes up that poison and makes them decidedly unpalatable to birds and other predators giving some immunity to attack.
They are not as common as they once were due possibly to the amount of 'Ragwort pulling' that now goes on. Ragwort is a plant that readily seeds itself and can spread very quickly so 'pulling' is the best way to keep it under control of sorts.