In a sign that east European migration to Britain may have peaked, the National Farmers' Union has told the immigration minister, Liam Byrne, that the numbers of EU migrants, including Poles, coming to Britain for harvesting jobs has dropped.

The shortage could see a rise in the price of strawberries.

A spokeswoman for Fruitful Jobs, a company which employs seasonal fruit pickers, said the problems were particularly acute this year.

"There is a shortage of fruit pickers from the UK and Poland," she said. "There has been a lot of negative press about the conditions the workers would have to put up with, which has put people off."

Last year, evidence compiled by the Transport and General Workers' Union alleged fruit pickers, mostly migrant workers from eastern Europe, worked 14-hour days, seven days a week, with only one 30-minute break a day.

According to the spokeswoman the good weather in Britain this year may also have played a part.

"The warm weather in April has dramatically brought forward the soft fruit season. Whereas a large percentage of students finish their courses in early June and begin fruit picking, we are having to find alternative sources of people," she said.

Philip Hudson, the NFU's chief horticultural adviser, said that Poles and other east Europeans were now less interested in coming.

"Their standard of living at home has increased more rapidly than anyone could have projected so they are now staying at home," he said. "Other countries, such as the Netherlands, have now opened their borders to them to work."

He said that 13 growers of soft fruit and salad vegetables needed 4,400 workers but were facing a shortfall of 2,400.

"There is a potential for crops to be left unharvested.

"We are talking about strawberries, raspberries and salad crops. I do not want to scaremonger but our real concern is that the harvest is going to be left in the field which will mean there will be less British produce in the supermarket."

The number of eastern Europeans coming to work in agriculture peaked at 22,700 in 2005 but dropped to 19,895 last year. The first three months of this year saw only 3,400 coming to Britain, well down on 12 months before.

The NFU wants to see an urgent increase in the seasonal agricultural workers quota and see the scheme expanded to other non-EU countries, such as Ukraine.

Farmers have already won the backing of Lord Rooker, the agriculture minister.

But Mr Byrne told the Guardian that the evidence that new European states could not fill Britain's labour shortages would have to be overwhelming for changes to be made.

"We are phasing out low-skilled migration from outside Europe because we think businesses should hire those close to home first," he said.