Hi Stephen, we suffer from Allium Leaf Miner and have done for some years. Our leeks don't look like yours. The miner lays something like a small dark brown grain of rice, which then starts off under the first layor of leek and heads for the roots. Once there, it moves in a layer and heads back up the stem, then down again and so on, stitching it's way in. They leave long thin orange stripes where they have been and I can't see these on your photos. If you cut the leeks open, you'll find the little blighters lurking within. The plant does keel over eventually, and it stinks, but it takes some time. You can pull what you think is a healthy leek, only to find you can only eat one side of it, if you are lucky. Most have to be binned. Hope this helps.