probably a leaf mining insect grub. not much you can do for it as once the hole is there the grub has already moved on.

Do you have access to food grade 3% hydrogen peroxide? I live in the States. You can mix up a bucket of water with a couple cups of hydrogen peroxide. Pour it out around the base of your laurel bush & let it soak into the ground. It won't harm your laurel bush, but it will destroy any dormant eggs and nasties living in the soil around the bush. HP has a very short 'life' and breaks down into oxygen & water - both of which are beneficial to your laurel bush anyway.

Thank you for your advice.
It was very helpful.

Bathgate, I have read with interest your reply regarding hydrogen peroxide. I have a problem with vine weevil in the ground. Vine weevil killer is very expensive in the UK and suggests that you only use it in container plants. So, what do you think about hydrogen peroxide as a solution for vine weevil eggs in the garden?

but you will also kill all the beneficial organisms in the soil that will affect the general health of the soil. It may break down into harmless water and oxygen but ask yourself why organisms have the enzymes to do this in the first place? It is toxic hence why it kills things.