(CNN) — Food shortages. Inadequate medical supplies. Civil unrest and road blockades. Lack of fuel. Delays at the border.
It's a scenario that travelers from around the world could be flying into if plans to crash out of the European Union are followed through.
That's enough to scare off Stephen Pickett, a sales director from Toronto.
"Why would I put myself out to go and get caught up in something?" he told CNN Travel. "This isn't something I want to put myself through."
Pickett, 47, has brought forward a planned November visit to October to avoid potential disruption. And he has put plans for further visits, as well as a move to London in December, on hold.
The UK is set to leave the EU at 11 p.m. October 31.
And while UK nationals are concerned about how it'll affect their travel plans -- a third of British travelers are concerned that flights to Europe might be disrupted, according to a survey this week from consumer group Which? -- travelers scheduled to fly into the UK have more pressing concerns.
Across six pages, the government document, nicknamed Operation Yellowhammer, details the potential on-the-ground outcome of a no-deal Brexit.
The UK government -- which was forced by Parliament to release the document after it was leaked to the Sunday Times newspaper -- insists Yellowhammer is a "reasonable worst case" scenario. Scottish First Minister Nicola Sturgeon, however, has said that the Scottish government was told the document was a "base scenario."
What's more, an industry expert has told CNN that in terms of travel, Yellowhammer looks "surprisingly optimistic" -- and that in the event of a no-deal, people could be waiting in border queues between the UK and the EU for days on end.
Queues at ports and airports could last 'days'
DANIEL LEAL-OLIVAS/AFP/Getty Images
Yellowhammer predicts "significant disruption lasting up to six months" for Channel crossings affecting food and medical supplies.
"Certain types of fresh food supply will decrease," it warns. Veterinary supplies may be interrupted, threatening outbreaks of disease among livestock, which could also affect the food chain.
Fuel supplies in London and southeast England would be disrupted, and could domino into shortages across the country.
It also warns of a "rise in public disorder," "protests and counter-protests," and road blockages.
"There's a lot more stability in Canada, so as much as London is great, why dip my toe into something when I don't know what'll happen?" said Pickett.
Although he married a British woman in August and was hoping to move to London at the end of the year, that's now on hold.
"The plan was to come the last week of November to assess where we wanted to live and make the move at Christmas," he said. "But I don't want to spend the money and not be able to go there because of civil unrest."
He and wife, Elizabeth, are now looking into whether it's easier for her to move to Canada, while he has brought his trip forward by a month.
"I wanted to get one more visit in before Brexit as we're not sure what's going to happen," he said.
"We don't know how easy it'll be to get in, what the queue will be like, or what the situation with food will be. And her parents are worried about supplies of their medication.
"If it goes on, I might be the person bringing everything over to them."
'If we were flying to Heathrow, I'd be terrified'
Travelers could find themselves camping out in airports.
DANIEL LEAL-OLIVAS/AFP/Getty Images
Pickett isn't the only traveler assessing their options. Grania O'Hare, who works for a tech company in Dublin and travels regularly to the UK, is due to fly to Yorkshire in November -- a trip booked before the Brexit date was set.
"There's definitely some slight trepidation, but we're flying into a regional airport," she said. "If we were flying into Heathrow, I'd be terrified."
She said she was less concerned about food and fuel shortages in the rural north of England.
"I'm a reasonable baker and I eat a lot of plant-based produce so as long as I have lentils and flour I'll be fine. But I have booked an extra bag for the hold, so we'll probably discuss a few days beforehand what food we should bring."
The bright side for O'Hare? If Operation Yellowhammer becomes reality, it's likely the pound will also plummet in value.
"I'll probably be hitting the duty free at the airport," she said. The UK's finance minister recently announced that duty-free purchases like alcohol and cigarettes would be re-introduced, post-Brexit, for travelers heading to Europe.
Border queues 'could last days'
Say goodbye to the fast track. Toughened border checks between the UK and the EU are likely to result in long lines.
Oli Scarff/Getty Images
Travelers should be less worried about riots and food shortages -- but they should have serious concerns about crossing between the UK and EU countries, says Tom Jenkins, CEO of ETOA, a trade association for tour operators in European destinations.
Jenkins, who is based in the UK, thinks a no deal is unlikely to happen -- British lawmakers have voted to make it illegal, so leaving without a deal would require Prime Minister Boris Johnson to break the law.
But if it does go ahead, he reckons the circumstances outlined in Yellowhammer would be "very restrained" and "surprisingly optimistic" when it comes to border crossings.
Guidance issued by the European Commission in November 2018 states that UK citizens entering Europe's 26-nation Schengen area will be treated as "third country nationals" at passport control -- on a par with travelers from other continents.
They will no longer be able to use fast-track lanes for EU citizens, and will be diverted into the lanes currently used by other nationalities, incurring more thorough checks. Passports will be inspected to see where else they have traveled, and they will be quizzed on the duration and purpose of their stay, and whether they have enough money to subsist.
"The implication is that everyone will be held up by at least 60 seconds, and due to the sheer volume of UK travelers to Europe, this will render all these processes difficult to deliver," said Jenkins.
"If you're arriving at Berlin Tegel [airport] on a flight from the UK, there might be two immigration lanes per aircraft, one for EU citizens, one for non-EU citizens.
"After a no-deal Brexit, the non-EU citizen line could be 200-strong. That's a wait of three hours.
"If you have five planes arriving at the same time, you've got huge problems.
"In Spain, where you have UK flights full of Brits landing every five minutes, it'll be something spectacular."
And he says that, while the delays won't affect EU nationals, who can still use the fast-track lanes -- as long as the UK doesn't impose reciprocal checks on them -- citizens of other countries will be caught up in the chaos.
"We're talking hours and hours in each airport for non-EU citizens," he said. "That isn't a worst case scenario -- it's a plausible worst case. European countries will enforce what they've been told they must enforce.
"The real worst case scenario is 24 hours of delay building up in the first 24 hours."
From there, he says it could spiral to "days-long" waits at passport control.
Although this shouldn't affect travelers making a trip to the UK alone, most non-EU nationals traveling to Europe for the first time pair the UK with the European mainland, says Jenkins. By far the best selling package that his tour operators shift is a twin-center London-Paris trip.
That, he says, is where everyone will be in for a "real shock" in the event of a no deal.
America stays positive -- unless there are riots
If the UK civil unrest becomes like that in Hong Kong, Americans will stop coming
Not everyone is so concerned. Tom Marchant, co-founder of luxury travel company Black Tomato, says that the tanking pound is proving popular with overseas clients this year.
"International clients are now going on the previously expensive trips which they'd been holding off booking, as they now see them as good value," he said.
Jack Ezon is founder of Embark Beyond Travel, a member of global travel agency network Virtuoso. "From an American perspective, we've been talking about this for three years," he told CNN.
"After the  referendum, we saw a dip in leisure travel to the UK. But there's been so much back and forth that now people are taking the approach of, '"I'm not going to cancel anything until I know what's going to happen.'"
His high-end clients will carry on visiting London, Brexit or not, because, he says, it's a business destination. With just one exception.
"If there are riots in the streets [after Brexit], I'm sure you'll see an immediate drop off."
He compares the potential situation to the current unrest in Hong Kong.
"Hong Kong is also a business destination, but people are moving their meetings to the Chinese mainland. Leisure travelers are shifting their base for Southeast Asia to Singapore or Bangkok.
"The budget market would be affected first. The bulk are not as well traveled, and are more fearful.
"The luxury market tends to be better traveled and more suspicious of media messaging, but if it gets to a point of so much noise, they would also move away.
"For us [Americans], going to London isn't a trip of a lifetime. It's not like going to Australia or on a safari you've invested so much in. Most are going for business or for three or four days. If you cancel the day before, it won't change your life."
One American who won't let the noise get to him is Ken Plunkett, a bar owner from Minneapolis.
He's flying to London on November 2, then on to Italy two days later, before returning home via London.
"I think it'll all work out," he told CNN. "If we have to wait for hours at the border, we have to wait. I won't cancel my trip.
"It reminds me of when we hit the year 2000 and we thought the whole world was going to crash, but nothing happened. I'm kind of taking that attitude."
Not even the prospect of civil unrest can put off Plunkett, who's been visiting Europe since 1965. He wouldn't go to Hong Kong right now because of anti-government protests, but says he'd still travel to London, even if there were riots.
"I understand the people of the UK," he told CNN. "They're not much different from us. We have protests and marches, and it doesn't stop people going to New York City or Washington DC. We're a country with laws and so is the UK.
"I'd give the UK more of a pass than I would other countries."
In the meantime, like Grania O'Hare, he's looking forward to a low-performing pound.
"Sure, I'll spend loads of money," he said. "I don't want to see anyone's economy crash for the few bucks that I'll save, but let's put it this way, we like the strong dollar."
"In the early days of the eurozone, Americans made huge pilgrimages because it was such good value compared to the dollar. People went two or three times a year.
"So assuming things are peaceful, it's a great opportunity to go shop and explore the UK."
A 'catastrophe' for travel
Up until now, it looked like the diminished pound was drawing visitors to a pre-Brexit Britain.
Figures released by Visit Britain show that flight bookings to the UK from September to November are up 5% overall year on year. Bookings from China are up 23%.
But Tom Jenkins, who works with tour operators from around the world, says that global markets frighten easier than the Americans.
"China is a fragile market, and I think that's totally reasonable," he said. "[Coming from] a different culture, you'd be radically affected by stories of disruption and interruption of supply."
And although he thinks that shortages of food, medicine and fuel will affect visitors far less than it does UK residents, he says it's bad optics.
"Food shortages and delays at the border don't make the UK seem a good place to go.
"No deal would be a straightforward catastrophe."