Liz
I have not had rust, but my garden has succumbed to allium leaf miner the past 18 months.
As I result, I decided to sow modules as Charles recommends, plant at very high density and start harvesting my Autumn Mammoth leeks mid August as younger plants so the crop is harvested before the disease danger period in late September/early October, which will also free up space for spring cabbage seedlings in late September.
So if you are really worried, you could just harvest some now and enjoy eating them in late summer! I just made onion, leek and potato soup, all freshly harvested produce….