British farmers fear they will struggle to find enough British labourers to harvest crops as a result of the Brexit vote, meaning food production will move overseas. If tighter immigration controls were brought in, the lack of access to labour would see British fruit and veg vanishing from supermarkets, say farmers.

"If you took migrant workers out of the supply chain you would within five days have no fresh British produce on the supermarket shelves," said Guy Poskitt, who grows 80,000 tons of carrots and parsnips a year in Yorkshire.

"My business would have to close, we could not serve our customers without the availability of migrant workers," he told Sky News.

Non-UK-born workers make up 65% of the agricultural workforce in Britain, compared to 5% in other industries.

The Farmers Weekly reports that 9% of growers experienced problems recruiting enough labour in 2015, according to an NFU survey, and some 66% expect reductions in labour availability by 2018, with 43% anticipating labour shortages.

About 90% of British fruit, vegetables and salads are picked, graded and packed by 60,000-70,000 workers from overseas, according to the Guardian.

Angus Davison, chairman at Haygrove, a major berry and cherry producer, employing 800 seasonal workers, told the Guardian that without foreign labourers, their growing would "move to the continent".

"We wouldn't be able to operate here in the UK because we would not be able to harvest the crops<' he said. "Do you want all your fresh produce to come from foreign countries? There would be more risks around its security, we wouldn't be as food secure as a nation."

Davison said his company had 15 workers a day applying to its offices in Romania and Bulgaria before the Brexit referendum, but this has fallen to one or two: "We are genuinely concerned. People over there are feeling they are not wanted here."

"UK agriculture cannot exist without foreign labour," farmer Robert Law told the BBC. "We haven't got enough staff of our own, particularly if you go further up north where the vegetables are grown."

Andrea Leadsom, speaking at a Tory conference fringe event, said that she saw no reason that Brexit should limit the number of foreign workers taking jobs in British agriculture, according to the Independent.

Asked if it was possible for Britons could do the jobs instead, she said: "Of course it is, that is a whole different issue.

"We could get British people doing those jobs and that tempts me to stray into the whole issue of why wages aren't higher and so on.

"My absolute hope is that with more apprenticeships, with more young people being encouraged to engage with countryside matters, that actually the concept of a career in food production is going to be much more appealing going forward."