What is it - unidentified caterpillar?

What is it - unidentified caterpillar?

Observation - What is it - unidentified caterpillar? - UK and Ireland. Description: In the greenhouse eating my tomato's leaves, seemed to be the only one there so I left it in peace. Did not see it again. About 30mm long

In the greenhouse eating my tomato's leaves, seemed to be the only one there so I left it in peace. Did not see it again. About 30mm long