Pesky Vermin or Not?

A slight change in tack for today's offering....

Does anyone know what this breed of caterpillar is before I remove them from the beech hedge plant in my front garden?

I am worried that if I don't remove it, I will give them an enormous lunch and my front hedge (which has to look fantastic as we live on Hedgerow Walk!!!) will be ruined!!!

So far the internet and Titchmarsh's book have failed to give me an answer - that and never minding the fact that I should, in fact actually, be doing some work!!!

All answers greatly received - I might try Simon Mayo and his drive time listeners, they are usually good at answering this sort of conundrum!