Can you identify this cocoon/caterpillar?

Can you identify this cocoon/caterpillar?

Observation - Can you identify this cocoon/caterpillar? - UK and Ireland. Description: I found a tiny caterpillar in the half rolled leaf tip of a nettle. It was green with a black stripe down its back. I didn't manage to take a photo before it pupated but it was tiny, about the thickness of a propelling pencil lead and maybe an inch in len

I found a tiny caterpillar in the half rolled leaf tip of a nettle. It was green with a black stripe down its back. I didn't manage to take a photo before it pupated but it was tiny, about the thickness of a propelling pencil lead and maybe an inch in length, I didn't see the whole thing. It pupated into a tiny what I think is a cocoon, only 9mm! It is brown and slightly ridged (looks similar to a mother of pearl cocoon only much smaller), does any one have any idea what it could be? Sorry the photo isn't very good as it is nestled in the fold of a leaf wrapped in silk and I didn't want to disturb it too much.
Thank you!