Allium leaf miner

Having recently moved to the South of England from the North, where I used to grow good leeks over winter, I was surprised to find my first crop here devastated by allium leaf miner. I have checked the RHS and other websites and can confirm the presence of small white maggots - the pupa stage.

Has anyone found a good way of dealing with this?

I think the only answer is to cover them with insect-proof mesh or fleece throughout the growing season - a pain when it comes to weeding but otherwise no leeks