They are bottling early this year at Château Bauduc. The shining, million-euro, steel-and-glass mobile bottling plant and its six-strong crew have arrived and are hard at work in a thin late-January sun: rinsing, drying, filling, capping, labelling.

“Last year, we didn’t bottle till March,” says Gavin Quinney, who with his wife, Angela, has been producing a range of critically acclaimed Bordeaux blanc white and Bordeaux supérieur red wines from their 25 hectares (62 acres) of vines since 2000.

“This year, we’ve brought it forward. We have to get enough stock, at least six months, into the UK before the end of March. It’d just be dumb not to. There’s no Brexit that’ll be good for this business. But a no-deal Brexit will be a catastrophe.”

Roughly 60% of the Quinneys’ production of about 150,000 bottles a year, all mis en bouteille – bottled – on the estate, goes to customers in Britain, where the restaurateurs Gordon Ramsay and Rick Stein have served Château Bauduc’s trademark sauvignon blanc as their house white for more than 15 years.

Bordeaux has 120,000 hectares of vineyards, and its 6,500 winemakers produce 750m bottles of wine a year. Photograph: Tim Graham/Getty Images

Quinney’s immediate concerns are technical and logistical, but crucial. The European commission and the British government have already confirmed that if the UK falls out of the EU without a deal on 29 March, Britain will leave the bloc’s electronic excise movement and control system (EMCS).

“The consequences of that don’t really bear thinking about,” he says. “It’s the online system for moving alcohol round Europe. It makes the business seamless, gets trucks through Calais and Dover with a minimum of checks, means governments are confident they’ll get their VAT and duty.”

Without EMCS, Quinney says, the only feasible fallback – until a new system arrives, which could take months or even years – will be pieces of paper, and pieces of paper spell long, long delays. “We know that no deal will mean logjams, complete chaos, at Calais and Dover for everyone,” he says.

“Pretty soon, it would be hard to find a transporter willing or able to take the job. Plus, in warm weather you really can’t have quality wine stuck for two or three days at the border unless it’s in refrigerated trucks, which cost a fortune. We have no option but to shift what stock we can now.”

EMCS is what makes it feasible – and profitable – for Adrian Munns to spend several days filling an articulated lorry with wine from more than 20 different Bordeaux producers, including Château Bauduc, then drive it, twice a month, to four or five different destinations in Britain.

“Without it, my job would be impossible,” says Munns, 62. “I’d just give up if that went, I think. Retire. I can’t imagine going back to the old forms; it’d be a nightmare. They won’t be able to come up with a similar system for years.”

Munns says Château Bauduc is far from alone in building up stock in Britain. For his UK trade customers, Quinney aims to have tens of thousands of bottles – at significant extra cost – stored in bonded warehousing by mid-March.

He is also launching a promotional deal for private customers, offering them duty and tax-free collection from a Calais warehouse before Brexit day. “Our bottom line is: buy your wine now,” he says. “Fill the garage and the spare room. Because frankly, nobody has the faintest clue what happens next.”

In his offices in an old stone wine warehouse on the Quai de Bacalan in central Bordeaux, Allan Sichel, the president of the Bordeaux Wine Council, which represents both the region’s 6,500 winemakers and the 300-odd wine merchants who market 75% of their output, says Quinney’s alarm is widely shared.

The industry is “very concerned indeed” by Brexit, and particularly the prospect of no deal, says Sichel, who also runs the family’s 135-year-old wine merchants. “When we know what we have to do, of course we’ll be able to do it,” he says. “But right now we don’t know what will change, and we may not have time to get ready for it.”

The UK is the fourth biggest global market for Bordeaux wines, accounting for nearly 24m bottles last year – a trade that dates back to the three centuries after 1154, when much of Aquitaine in south-west France was ruled by the kings of England and profits from the sale of clairet, or claret, were the crown’s main source of income.

Thierry Decré: British fine wine merchants have ‘bought wisely and hold plenty of good stock’. Photograph: Jon Henley

There is “real passion for our wines in Britain, and a huge amount of expertise”, says Sichel. But the impact of Brexit is “already perceptible. Buyers are building up stock, but also asking for delays on their payments … The pound is weak, UK duty is high. They want us to absorb some of the costs. There’s already pressure.”

Significant delays at Calais, with trucks blocked for two to three days awaiting customs clearance and regulatory inspections, would “add exponentially to everyone’s costs, and inevitably end up reducing demand”, Sichel says. “That’s just not tenable. And any further big falls in sterling would be disastrous.”

The premium market, which accounts for at most 5% of Bordeaux’s production, is unlikely to be affected, says Thierry Decré of LD Vins, which specialises in fine wines produced by some of Bordeaux’s best known chateaux and sold to top UK wholesalers, such as Farr Vintners and Berry Bros & Rudd.

British fine wine merchants have “bought wisely and hold plenty of good stock”, Decré says. Besides, those happy to pay €100-plus for a bottle of wine – let alone €2,500 for a bottle of Château Pétrus, or the €480,000 recently fetched by a 1945 Romanée-Conti – “will not suffer greatly from Brexit”.

Philippe Castéja, of the leading Bordeaux wine merchants and château-owners Borie-Manoux, says he is “not overly concerned … The chaos of a no deal would be so enormous that it simply couldn’t last – Britain wouldn’t survive. They’d have to sort it out. It’ll be rather complicated for everyone for a few months, though, no doubt.”

But back at Château Bauduc, Quinney is – like many Bordeaux producers – equally worried by the impact on his business of even a negotiated UK departure from the EU. “Anyone in the wine trade will tell you: it was tough before Brexit,” he says.

“An intensely competitive market, already hit hard by the low pound and high duty. If we’re also out of EU regulatory alignment, the customs union, the single market … It’s just a whole load of unwanted extra hassle, for everyone. Some people are going to ask if it’s worth it. You wouldn’t have these problems selling to Belgium.”

As a non-essential product, UK wine sales will inevitably be hit by any post-Brexit fall in consumer spending power or confidence, Quinney is sure. If that is accompanied by transport problems and customs delays for producers, the whole shape of the business might change .

“Some will look elsewhere,” he says. “The market for mid-range, estate-bottled wine in the UK could collapse. Producers may start shipping lower-grade wines in bulk and bottling it in the UK, like the Australians do now. Bordeaux might become a port again, who knows? People will try to be creative. But, yes, it’s going to be very tough.”

Britain, Bordeaux and wine

The UK is the world’s second largest importer of wine , importing 12m hectolitres (263m gallons) annually to about 36 million consumers .

Average consumption is approximately 20 litres a head .

Eight countries have at least a 5% share in this highly competitive market: Italy (3m hl), Australia (2.1m hl), France (1.7m hl), Spain (1.3m hl), Chile/US /South Africa (all around 1.1m hl), New Zealand (0.8m hl), Germany (0.7m hl).

Bordeaux has 120,000 hectares of vineyards, and its 6,500 winemakers produce 750m bottles of wine a year.

Sales of Bordeaux to the UK in the 12 months to the end of November 2018: 1 79,696 hl , which is nearly 24m bottles – roughly 8% of total Bordeaux volume and 10% of total value.

The UK is Bordeaux’s fourth-biggest global market after China, the US and (just bigger) Belgium.

• This article was amended on 11 February and 5 March 2019 to correct figures for UK imports of wine from New Zealand and Germany: 0.8m hl and 0.7m hl respectively, not 800m hl and 700m hl as stated in an earlier version.