Pick them off if there aren't too many, otherwise the only thing you can do is spray with soapy water and remember to wash well before use. Is the mesh small enough to ensure that no insects can get through it and is it lifted away from the actual plants.

Also try planting the wild Malva among the cabbages. Diane bulley gave me this tip and it works - the butterflies hover over the cabbages but don't land. Though its hard to understand how the caterpillars got there!

Depends on the size of the mesh Stera., it is more usual to protect a raised bed from damage with a thin fleece.

True - mesh needs to be too small for butterflies.