The recommendation was made in a report published last week to advise the Government on which shortages of skilled labour can sensibly be filled through immigration.
Staff at the University of Liverpool, which conducted the study, said 92 per cent of the 268 farmers surveyed expect to experience recruitment problems in the future and 73 per cent discussed the problem of getting seasonal labour.
The report said: "Farmers ... were concerned that the loss of SAWS in 2010 would only magnify the problem of labour availability at harvest time." It concluded: "There will always be a demand for temporary agricultural labour ... this demand is most likely to be met through immigration.
"An improved version of SAWS extending beyond the EU is well suited to meeting this demand and is currently being discussed at an EU level via the proposed directive on 'Entry Conditions and Residence of Seasonal Workers from Third (World) Countries', set to be published in late 2008."
Chairman of the NFU board for horticulture Richard Hirst welcomed the findings. "We will keep pushing this point and all the other facts about seasonal labour in the hope that eventually the Home Office will realise it needs to alter its stance," he said.
British Summer Fruits chairman Laurence Olins said: "The report reinforces the importance of SAWS to the horticultural sector. Without a change to the existing restrictive rules, British growers may not be able to meet the growing consumer demand for home-grown soft fruit."