In the event of a no-deal Brexit, Boris Johnson is reportedly planning to buy almost the entirety of Wales’s lambs.

Quite what the Prime Minister plans to do with £500m of lambs is not clear. “Are we going to give schoolchildren lamb stew, but no fruit and vegetables?” asks an audibly frustrated Tim Lang, a professor of food policy at London’s City University.

Lang raises a worryingly valid point. The government’s seemingly bizarre mass-sheep-buying plan is a bid to appease Welsh farmers, who currently sell 92 per cent of their slaughter to EU member states, and who would be hit by a 40 per cent export tariff if the UK leaves the bloc without a deal.

But in the event of a no-deal Brexit, Johnson will have far bigger problems on his plate – or not, as it were – than irate farmers.

Should the UK crash out of the EU without a deal on 31 October, as Johnson has repeatedly insisted that it could do, the number of lorries entering the UK will fall by at least a third the following day, explains Lang. This will cause the amount of food we import from the EU and countries with EU trade deals to drop by around 50 per cent.

According to Lang, these are neither so-called Remainer scaremongering tactics nor his own predictions; they are the eventualities the government – and food industry – are expecting.

In a paper entitled “No-deal food planning in UK Brexit”, which was published last week in medical journal the Lancet, Lang called on Boris Johnson and his government to be honest with the public about the realities of a no-deal Brexit.

The fears outlined in this paper were echoed by Tim Rycroft, the head of the Food and Drinks Federation. Speaking last week on Radio 4’s Today show, he described a no-deal Brexit as a “disastrous outcome”, explaining “there will be selective shortages, and they will be to some extent random because it depends on which trucks get through”.

Random though they may be, it seems likely that among the worst affected would be supplies of fresh fruit and vegetables.

Just 55 per cent of the vegetables consumed in the UK are produced here, and less than 12 per cent of the fruit. For the rest, we rely on imports – most of which come from the EU. Any post-Brexit shortfall will be made worse by the fact that 31 October coincides perfectly with the end of the British agricultural growing season; when there is an already reduced availability of domestic fresh produce.

In inflicting a shortage of fresh produce on the UK, Lang accused the government of “flouting the advice of Public Health England”, claiming that it would not be posssible for people to eat the recommended five portions of fruit and vegetables a day.

The government is preparing for the disruption to imports and exports to continue for three months, covering the entire Christmas period, Lang wrote in his paper. Even by the 31 January 2020, it expects that food supplies will at best have returned to two-thirds of their pre-Brexit levels.

Asked whether Lang himself agrees with the government’s predictions, he is firm in his answer. “Yes, everyone in the food industry thinks this, I've been learning all of it on the know. Basically the food industry confirms this is what they expect to happen.”

Such intense food shortages, almost overnight, will have one obvious outcome: price rises. But this is where Lang disagrees with Johnson’s government, which is expecting an increase of 10 per cent.

“I think it will be higher,” he tells me. “As I said in my article, in the 14-page document prepared by the Cabinet Office – widely presumed to be what made Boris Johnson look ashen-faced when he came out of a briefing – Sir Mark [Sedwill, the cabinet secretary and national security adviser] said 10 per cent food price rises.

“Most people in the food industry think [10 per cent] at least,” he says, with a heavy emphasis on the last two words. “And it depends on the level of the pound, of course. The pound is going down already.”

Whatever the price hikes, those on low incomes will inevitably be hardest hit – likely in a manner that leaves them unable to afford what little fruit and veg makes it to our supermarket shelves.

In his paper Lang wrote how foodbanks have already warned that in the event of a no-deal Brexit they won’t have the food, volunteers, or storage capacity to deal with an increase in people relying on their services. Many fear that donations from the public would also dry up as supplies dwindle and become more expensive.

Last month, Sustain, an alliance of charities and organisations related to food and farming, wrote to Michael Gove, the minister charged with no-deal planning, and Amber Rudd, the Work and Pensions Secretary, called for the establishment of a national hardship fund if the UK leaves the EU without a deal.

This would help vulnerable people afford food and other basic supplies. But it is not just those on low incomes who will be affected. Research published earlier this year by Sustain suggests that children, hospital patients, people in care, prisoners and others in public sector institutions are all also particularly likely to go hungry if food supplies are disrupted.

With such bleak expectations and no support from the government, many are looking to prepare for a no-deal Brexit themselves – but Lang would urge against it. “I've said consistently I'm not in favour of stockpiling because it adds to the volatility of the situation,” he explains. “But I entirely understand people if they do.”

Really, though, what we need is for the government to be honest with people about the realities of a leaving the EU without a deal. Polling by Statista last month suggests that 26 per cent of the public are in favour of a no-deal Brexit. Would they still be if they knew the realities: empty cupboards, empty supermarkets, and vulnerable people going hungry?