On a chain-link fence beside a wet and windswept road in northern Belgium, a banner flaps bravely against the squalls whipping in from an angry sea. “Your gateway to the UK,” it proclaims, in English. “Brexit-proof Zeebrugge.”

That’s the plan, anyway. Since nobody in either the North Sea port or the small beach resort next to it knows what Brexit will actually look like yet, the promise may be something of a hostage to fortune. But they are working on it.

“We have to,” said the veteran customs official manning a newly-opened Brexit information point across the sodden and sprawling trailer park. “Half this port’s business is with Britain. Five thousand jobs. It could have a massive impact here.”

Whatever kind of Brexit emerges, it will touch all whose livelihoods have – for the past quarter-century – been conditioned by Europe’s borderless single market, and few more so than the communities on both sides of the Channel that are directly involved in trade between Britain and the continent.

On Heiststraat, all neat brick houses and gabled shopfronts, Mathilde Backer, who works in marketing for a hotel in nearby Bruges, said she had frankly not got the faintest idea what Brexit might mean for Zeebrugge. “But it’s clear anything that’s bad for the port will probably be bad for the town,” she said.

Facebook Twitter Pinterest Goods are moved around a computerised warehouse in Zeebrugge. Photograph: Jasper Juinen/Bloomberg/via Getty Images

Jeroen, her partner, worked off and on for the fish auction, Backer said, one of Europe’s largest: “More than half of what’s sold there is caught in British waters, and nobody knows who’s going to be able to fish where after Brexit. That’s pretty crazy, isn’t it?”

If officials in the port, built a century ago to reconnect medieval Bruges with the sea, are confident there can be no return to the weighty armfuls of paperwork and endless checkpoint waits of pre-single market days, some worry about a longer-term impact on the town.

“Technically, we’ll be as ready as we can be,” said Michael Voet of the local dockworkers’ union, in his office on the waterfront by the old fishing harbour. “But Brits will surely be buying less, that’s my big fear. Our members are paid by the day so that’s less money for them, and less to be spent here.”

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Everything from washing-up liquid to just-in-time engine parts, from orange juice to Evian mineral water – plus getting on for a million new cars a year – passes through Zeebrugge on its way to the UK, on 60-odd weekly sailings to such ports as Sheerness and Tilbury, Southampton and Hull.

The Belgian port has one card up its sleeve: it handles mostly unaccompanied freight, so hopes to be less hit by any new post-Brexit border formalities and checks than places such as Calais, which mainly process trucks with paper-intensive drivers.

“We’re trying to minimise future disruptions; there’s extra staff, a new platform to pre-process everything electronically,” said the customs official, who preferred not to be named. “But it’s still a load of extra work right now – and we don’t know exactly what we’re preparing for.”

Facebook Twitter Pinterest A lorry driver, right, assists a customs worker checking a shipment of goods made in China at the Port of Zeebrugge. Photograph: Jasper Juinen/Bloomberg/via Getty Images

Even the resort’s principle tourist attraction, the Seafront theme park, deserted in the November near-gale, had a moment of Brexit uncertainty, said manager Sofie Peeters. Only about 5% of her 50,000 annual visitors come from Britain, so any decline in their numbers would not make much difference.

“But only the other day,” Peeters said, “I got a catalogue of cuddly toys – the kind of thing that sells quite well in the souvenir shop – from a UK company. My first thought was: I wonder if there’s going to be some sort of import duty on these after Brexit?”

On board the Pride of Bruges, one of the two P&O ferries that alternate the daily 12-hour crossing from Zeebrugge to Hull, British truck drivers were downbeat. “If things go back to anything like what they were before, it’ll cripple the industry,” said Ian Vear, taking a lorry-load of Belgian beer back to Yorkshire.

Cradling a bottle of something else in the Lounge bar, Vear, who has been driving for 31 years, said truckers heading for the continent before 1993 had to “get our papers inspected and stamped and our tanks dipped – to see we weren’t carrying too much fuel – at every border. A four-day job took eight.”

There were advantages, said Sam Campbell, carrying Nissan car parts to Sunderland. “You’d get to Spain or Italy on a Friday and know you wouldn’t clear customs till Sunday. So, the beach … But then it could take you ten hours to get through Dover. If that’s Brexit, I’d quit.”

Several had voted leave. “I felt more strongly about our borders,” said Campbell. “And I never thought it would pass. Brexit could wreck my job, but it’s wrecked anyway. Just-in-time, you’re tracked every second of the way. And we can’t compete with Poles, Latvians, Romanians, Bulgarians … They work for half pay, less.”

Facebook Twitter Pinterest Ferries at Hull. Photograph: Arterra/UIG via Getty Images

‘Doc’ Lockyer, from Hull, now a jobbing driver after running his own haulage business for 3o years, was a lone optimist. “It’ll be all right eventually,” he insisted. “Provided we adapt and use the technology right, it can be done. People are exaggerating the problems for their own agenda.”

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Ten hours later, June Heritage, 72, from Darlington, was stepping unsteadily down the gangplank into a chill, damp Hull morning. She, too, had voted leave: “Enough’s enough.” But she’d enjoyed her coach trip to Bruges Christmas market and couldn’t see Brexit changing much. “People will still want their fun, won’t they?” she said.

A blustery walk up the road at Associated British Ports, which runs Hull and the three other Humber ports – employing, directly and indirectly, 23,000 overwhelmingly local people – head of corporate affairs Dafydd Williams agreed.

“The issue,” Williams said, “is going to be goods, not people.” He saw one possible upside from Brexit for Hull: container traffic grew 16% last year, with sailings up from five to 15 a week – part of a noticeable Brexit-driven shift in trade from southeastern ports, such as Dover, to the north-east.

Facebook Twitter Pinterest The marine control centre in the King George Dock in Hull. Photograph: Arterra/UIG via Getty Images

“The longer sailing times used to put people off,” Williams said. “But if you’re going to be stuck in a queue at Calais or Dover...” Persistent uncertainty, and the possible earthquake of no deal, were still a worry, but the Humber ports were “cautiously optimistic. We’re investing, and we’ll deal with whatever comes.”

Among ABP’s investments was, jointly with Siemens, a hefty punt on £310m Green Port Hull, making wind-turbine blades and servicing offshore windfarms. Juergen Maier, the German company’s UK chief executive, and an outspoken remainer, has just backed Theresa May’s deal as providing “certainty after two very difficult years”.

Townspeople remain, perhaps inevitably, divided. Hull, Britain’s third most deprived local authority, voted 66% for Brexit in 2016 – even if recent polling suggests that number has fallen substantially and at least one of the city’s three Labour-held constituencies would now support remain.

On blustery Jameson Street, opposite the railway station, Rob Bateson, an IT worker for a Scandinavian-owned timber importer, said the vote was a “historic mistake. This is a port city, we grew by trading with Europe. I can already see it in my job – it’s going to throw a massive spanner in the works.”

But Steve Todd, a retired welder, said the only mistake had been to “not get out straight away, and sort the shit out afterwards. Now we’re stuck.”

And Aida Hesketh, a payroll assistant for a temp agency, said none of her reasons for voting leave had gone away. “We’re being dictated to, there’s too many Europeans here, and it’s not right,” she said. “Whatever, we need to get out.”

• This article was amended on 12 December 2018 to clarify that The Pride of Bruges ferry is one of two alternating vessels making the Zeebrugge -Hull crossing.