One of Britain's largest berry farmers has moved part of its business to China due to a labor shortage, as thousands of seasonal workers stop coming to the United Kingdom following its vote to leave the European Union.

Herefordshire-based Haygrove has reduced its English seasonal workforce from 1,150 to 950 and moved some operations to Yunnan province, Southwest China, where it will grow raspberries and blueberries for the Chinese market.

"We're reducing our employment this year by 200 people - 20 percent of our workforce - in anticipation of problems we can't afford and we are investing in China instead," Haygrove founder Angus Davison told The Guardian.

Around 4,300 - or 12.5 percent of seasonal British farm job vacancies were unfilled last year, according to data from the National Farmers Union.

UK agriculture relies heavily on overseas labor - around 99 percent of seasonal workers come from Eastern Europe, with just 0.06 percent being British.

Davison has written to British Prime Minister Theresa May calling for action.

"Unless a seasonal workers scheme is put in place, you must expect to see the steep decline of this significant rural employer and source of food," he wrote.

Last year was the first time since the NFU began surveys that the industry experienced a job shortage, and as a result, union deputy president Minette Batters said food was left "rotting in the field".

Tom Keen, NFU international trade and EU exit advisor, said European workers are establishing relationships with farmers elsewhere instead. Sterling's decreasing value since the referendum decision is another factor.

"There is also a feeling of 'do people want me here?' The general atmosphere has changed and some will not feel particularly welcome here," Keen said.

Sectors struggling

Industry sectors that rely heavily on overseas permanent workers - including dairy and poultry processing - are also struggling, he added.

"It's really worrying. We hear stories of businesses reducing their production. With horticulture it is a case of not putting down new plants. In the poultry industry, people aren't getting as many chicks in to rear. This is the action that farms are taking because it's too much of a risk."

The NFU and 35 other food organizations co-signed a letter published in this weekend's Sunday Times, calling on the government to maintain "free and frictionless" trade with the EU, and ensure access to an adequate labor supply.