As England’s largest agricultural jamboree, the Royal Norfolk Show normally functions as a shop window for the country’s farming prowess. But this year it also offered a glimpse of the problems facing a post-Brexit nation. In the showground, amid displays of fresh fruit, vegetables and prize-worthy bulls, the talk was of how farmers would find the workers to harvest their crops in a world cut off from Brussels and free movement of labour.

In the wake of the Leave vote, there was now a “serious question mark” over the fruit industry’s ability to staff harvest season, warned Laurence Olins, who chairs British Summer Fruits, the sector’s trade association.

Soft fruit producers relied on workers from the continent, he said, and a vote for restrictions on migrant labour would have consequences because no British nationals wanted to do the work.

Among the produce savoured by nearly 100,000 attendees at the Norfolk Showground, six miles west of Norwich, were sweet English strawberries. But according to Olins, our taste for the fruit is not matched by a willingness to earn money from harvesting it – a process that requires 50,000 seasonal workers.

“UK residents do not have the appetite to work in our fields and packhouses on a seasonal basis,” he said. And it is EU workers, travelling unimpeded to the UK, who fill the labour gap.

The labour force picking soft fruit in Britain come mainly from overseas EU countries. Photograph: Kelvin Murray/Getty Images

“If our current pool of labour is to be severely curtailed, or prohibited in future, the whole viability of our home-grown industry will be at risk” Olins said.

He added that a diminished workforce would mean less in the way of homegrown crops, more imports – and therefore higher prices. It is also possible that British farmers will simply follow the labour and move their production abroad – to the Netherlands or Portugal.

Anecdotal evidence points to a looming labour crunch for the fruit and vegetable sector – worth £1.2bn a year – if the new prime minister triggers article 50 to leave the EU and targets restrictions on immigration as part of a new deal with Brussels. One grower member in Kent has a permanent workforce of 800 people – all migrants from EU countries.

Another major employer of migrants is Staple Vegetables, near Boston, Lincolnshire. Its 10,000-acre farm and packing site has up to 1,000 workers on its books at any time and the majority are from overseas.

The Food and Drink Federation, which represents nearly 7,000 businesses – from major brands such as Britvic and Mr Kipling to the kind of smaller-scale producers who had come to the show – warned that the food and drink industry faced huge uncertainty following the vote. The FDF says its members employ 130,000 people – more than a quarter of its 450,000-strong workforce – from eastern Europe.

There were some optimistic voices amid the gloom. A positive post-Brexit message came from Kathy Thompson of Chillis Galore, who makes jellies and sauces from fresh chillies at her home in Drayton, near Norwich. She said the decision to vote leave could not have come soon enough: “We need to be free of red tape and bureaucracy, and take control again.”

As cows adorned with colourful rosettes were paraded around the show rings in the Wednesday morning sunshine, farmers just yards away – in a display area sponsored by Suffolk brewer Adnams – were debating the impact of Brexit. The talk was of little else as the ale was downed.

Among those taking part that morning were the National Farmers’ Union president Meurig Raymond and Liz Truss, secretary of state for the environment, food and rural affairs. Raymond urged Truss to deliver a new agricultural policy that worked for British farmers, consumers and the economy as they discussed how agricultural interests should be represented at Brexit talks in Brussels.

“The country has spoken and we need to respect the views of people through the democratic process,” said Raymond, who has warned of food price rises in the wake of a Leave vote. “Even after article 50 is triggered, we will have two years before we exit. That will give us time to formulate the right policy for British farming.

Meurig Raymond of the NFU said the two years until Brexit give time to formulate a farming policy for Britain. Photograph: Aled Llywelyn/Athena

“Norfolk is such a diverse county, with fantastic livestock, combinable crops and vegetables. We can produce anything in this part of the world. So this needs to be an opportunity.”

On Friday the NFU said it would launch a consultation on the impact of Brexit and what a new farming policy should look like. The prevailing mood among businesses and visitors at the show was a resolve to soldier on and make the best of the new situation while trying to keep local economies thriving.

The chatter in the main food tent reflected worries about food prices going up, instability caused by the loss of £3bn of annual EU subsidies for arable farmers and access to the single market – and even redundancies in the 40,000 strong agricultural workforce in Norfolk. But others were hopeful that being out of Europe could ultimately make the farming industry stronger.

“The mood has changed completely,” said Clarke Willis, chief executive of Anglia Farmers, an agricultural purchasing co-operative. “We woke up on Friday morning to shock and disbelief. But we now have to grasp the opportunity, roll up our sleeves and work together.”

Louisa Kiddell, who runs the Gluten-free Shop and Cafe in Norwich, said that while she was still reeling from the result , prices from suppliers had started to go up. “My wholefood suppliers put up their prices earlier this week, which was a bit of a surprise and means I have to look at my own pricing,” she said.

Farmer Clive Salmon, who voted leave, and his son, Ed. Photograph: David Levene/The Guardian

In the show’s food hall, it was not just fruit and vegetable suppliers who were worried. Roger Kelsey, chief executive of the National Federation of Meat & Food Traders, who has a background as an independent butcher and was hoping to encourage young people to look at training opportunities in the sector, said the UK meat industry relied heavily on migrant labour. “It would not survive without them,” he said. “Go into any abattoir or meat processing factory in the east of England – or anywhere in the UK – and you will see Polish and Portuguese workers helping the slaughtermen and doing what are seen as the unpleasant jobs, such as evisceration.”

The debate over Brexit and its consequences will last years. Many of the show’s attendees came from farms whose operation spanned generations, including Clive Salmon and his 25-year-old son Ed. Clive, who voted to leave, sold his farm two years ago, although he is still involved in breeding prize-winning livestock.“I think there is a future for farming, though it may take a while to get there,” he said. “I’m very glad I sold when I did.”