September's harvest, which accounts for 55 per cent of the UK crop, was two weeks late but quality remained good.
But onions harvested from mid-October to the present - around 20 per cent of the crop - have seen poor harvest conditions, with some staining and thick necks, and are described as having poor storage potential.
"The considerable investment made by growers in new stores and technology puts us in a strong position to meet these storage challenges," British Onions chairman John Patrick said.
But he added: "It is crucial that the packing industry and retailers recognise that size and specifications need to be managed to maximise utilisation. This will help protect against a hype in the market in the New Year and also maximise farm gate return, in a year where production costs per tonne have escalated."
Sales remain good across all sectors, according to British Onions. "Hopefully by making small changes early, we can continue to deliver quality for final consumers, while keeping UK product on the shelf for the normal window," it added.