I have only had the plot a couple of years and was told that onions had been fine on it with previous grower so have tried several places and sadly all appear to be infected. I can salvage and eat some of the leeks as not badly infected and it does appear to be odd clumps not the whole crop.
https://www.rhs.org.uk/advice/profile?pid=226 this made me think it was less likley at this time of year. SO looks like I will not be growing alliums for the next 15 years 