Could be Burnet Moth larvae, but that's usually found on ragwort and other Senecio. They strip ragwort to a skeleton!

My thoughts exactly but do they eat anything else? What plants are they on please?

Or, Cinnabar moth, they are very similar.

Try and be kind, butterflies and moths are in decline as it is.

Thanks to you all, they are on and have stripped all my super Senettis. This has happened over the past couple of weeks. No worry Honeysuckle I will move them on rather than hurt them!!!

I don't think it is Burnet moth because the dark stripes on that caterpillar are segmented and it is quite hairy.

That said, cinnabar moth caterpillars are always said to only feed on ragwort, that's why it is such an important plant.

Intrigued I just spent ages looking on google and failed to come up with anything else similar in Britain.
Might be an idea to grow something else next year and hope the culprits fly off somewhere else.