Butterfly or moth caterpillar?

Butterfly or moth caterpillar?

Observation - Butterfly or moth caterpillar?. Description: Found while digging in garden. It was put onto paving slab where it soon unrolled and headed off down a crack. Approx 30mm long. Help with ID would be much appreciated.

Found while digging in garden. It was put onto paving slab where it soon unrolled and headed off down a crack. Approx 30mm long. Help with ID would be much appreciated.