[Aidy]

Is rife amongst our leeks this year on site 

We/ I have never experienced this before in all my years of growing. I noticed a few nobbled leeks and i pulled them they were full of maggots.

Most other plots are also suffering with it.

[mumofstig]

It's a real pain isn't it - we've had it for the last few years - sometimes just for a change we'd get Allium Leaf Miner instead. *sigh*
Have to grow them under environmesh now, to make sure of getting any 

[Salmo]

May not be onion fly maggots. Could be leek moth caterpillars. Look closely at the grubs with a hand lens. If they have a head and legs they are caterpillars. Onion fly grubs are maggots and have no head or legs. Look at leek moth on google images.

[Aidy]

May not be onion fly maggots. Could be leek moth caterpillars. Look closely at the grubs with a hand lens. If they have a head and legs they are caterpillars. Onion fly grubs are maggots and have no head or legs. Look at leek moth on google images.

Looking at the RHS fact sheet I believe it is the allium leaf miner.