A leading independent East Anglian-based farmer-run research charity has set up a task-force to investigate the big variation in wheat yields.

While very low levels of sunlight were recorded as grain crops were ripening in June and July, levels of disease were also the worst for decades, said Cambridge-based cereal researcher Bill Clark.

“The bottom line is that radiation levels were low at 60 to 70pc of normal levels in June and July, which is why yields were low. It is almost as simple as that,” he said.

But the research body, NIAB TAG (National Institute for Agricultural Botany) found big variations. “It was region to region and field to field even adjacent fields and we’re trying to understand the reasons,” he added.

Harvest yields from field-scale wheat crops at the Morley Agricultural Foundation’s farm, near Wymondham, where many of its trials were carried out, illustrated the puzzle. Farm manager David Jones, said: “Half was very good, the other half was indifferent quality.”

One variety yielded about 10 tonnes per hectare but another, Oakley, which was the highest yielder for the past five years, produced one of the worst at just eight tonnes per hectare, he said.

Mr Clark, who has more than 30 years’ experience researching arable crops, added: “This has been the worst disease year that I’ve ever known. Farmers have had this double-whammy of low yields and then disease on top of that. They’ve spent a lot of money on fungicides trying to control diseases and still got low yields. They feel doubly aggrieved.”

He would be studying yield results from farmers representing 20pc of the national cereal acreage as part of the research. Mr Clark recognised that wheat yields have been on a plateau and that some early-drilled wheat crops did not perform as well as some later drilled crops.

“There is some evidence that yields in trials are going up but not on farms. That’s a picture across the whole of Europe and into the United States,” he added.

Results from this season’s HGCA’s autumn wheat bulb fly survey suggest that the risk from this pest is relatively low. In fact, the overall risk this year is equal to the lowest level risk ever recorded in 1984.

A total of 30 fields were sampled. The sites were split across eastern and northern England, where the pest is historically most prevalent. Only one field was classified as ‘high-risk’, containing egg numbers greater than 250 per sq metre threshold.

“It is likely that the cold and wet weather had an impact on the number of adult flies and their ability to lay eggs,” stated Caroline Nicholls, HGCA Research & KT Manager.