Douro Valley, Portugal - 12 September, 2018

1. Pan of Douro River near Pinhao, Douro Valley

2. Wide of slope with green vines

3. Mid of Ferreira port wine slope

4. Mid of Alves de Sousa port wine slope

5. Wide of protected landscape with sign

6. Close of sign reading (Portuguese) "Douro Wine Valley, World Heritage"

7. Change of focus from slope to vine leaf

8. Workers arriving to harvest

9. Tilt up from bucket to workers going up the hill

10. Close of bucket with grapes

11. Mid of workers

12. Close of worker cutting vines

13. Close of bucket filled with grapes

14. Tilt down from sun to workers walking

15. Set up shot for Jose Pereira, foreman of Rozes port wine producer

16. SOUNDBITE (Portuguese) Jose Pereira, foreman of Rozes port wine producer:

"If it wasn't for wine there would be a crisis, both for our employers and for us. Without the wine the Douro region would be on its knees. Wine is our wealth."

17. Tractor carrying grapes up hill

18. Wide of Quinta da Gricha entrance

19. Workers receiving and processing grapes from the harvest for Churchill's port wine production house

20. Various of grapes being processed

21. Tilt down of Rozes wine barrels

22. Wide of old bottles of port wine

23. Change of focus between vintage port wine bottles

24. SOUNDBITE (Portuguese) Luciano Madureira, oenologist, Rozes port wine production:

"Port wine is good because it's from here, from this region. This is a unique region, where people are very important, the climate, the soil – which is not very rich, eager to produce more but that can't give more than what it already gives. We are in the mountains so what we do is always in small scale but with extraordinary quality."

Vila Nova de Gaia, Portugal - 11 September, 2018

25. Entrance to Taylor's port wine cellars house

26. Close of Taylor's symbol

27. Wide of wine barrels at cellar

28. Set up shots for Taylor's managing director Adrian Bridge

29. SOUNDBITE (English) Adrian Bridge, Managing Director, Taylor's port wine house:

"Well, I think that clearly when we are selling a product like Port - which we have done for hundreds of years – we have seen many disruptions, of war and pestilence over the centuries and perhaps if one puts the context of Brexit in these terms of an unfortunate blip that may cause some problems and probably requires some degree of readjustment, I think that would be fair."

30. Wide of royal warrant of appointment

31. Close of royal warrant of appointment reading (English) "By appointment to H.M. Queen Elizabeth II suppliers of Port Wine, Taylor's Port Portugal"

London, UK - 14 September, 2018

32. Various set up shots of Enrico Bonadio, Senior Lecturer in intellectual property law at City, University of London

33. SOUNDBITE (English) Enrico Bonadio, Senior Lecturer in intellectual property law at City, University of London:

"I don't think the Europeans will accept, the EU will accept a Brexit deal which does not protect feta cheese, Parmesan cheese or champagne wine also because the entire final Brexit deal will need to be ratified by national parliaments, 27 national parliaments. Can we imagine the Greek parliament or the Italian parliament or the French parliament having to ratify a final Brexit deal that does not strongly protect feta, parmesan or champagne? It will be difficult. That's why a deadlock on this issue could jeopardize the entire Brexit deal."

London, UK - 19 September, 2018

34. Wide shot of the Raymond Reynolds stall at "The Dirty Dozen" wine and spirits tasting event in Glazier Hall, London

35. Attendee tasting a wine

36. Pan up from bottles of Niepoort port wine to wine tasters

37. Close up of wine being poured

38. Shot of Raymond Reynolds pouring some Niepoort Bioma port

39. Cutaway corks

40. SOUNDBITE: (English) Raymond Reynolds, Owner of Raymond Reynolds Ltd, a specialist UK Wine importer:

"I don't have any fear in that sense (of Geographical Identification ending after Brexit) because you know your sources of supply, we work with our growers, there is a historic link. They are trusted in terms of their quality and through to retailers and consumers that works as well so the only problem with Brexit is the uncertainty."

41. Tilt up of bottle of port

42. Various of Raymond Reynolds with customers

The scorching late summer sun of northern Portugal is ripening the black, super-sweet grapes that will go to make what European Union rules say is the only wine that can be called port.

Wine making has for several centuries been a way of life for many families here in the picturesque valley of the River Douro. It's a tradition the EU regulations are designed to protect.

"If it wasn't for wine, the Douro region would be on its knees," says 59-year-old Jose Pereira, a foreman for the Rozes port wine producer, as behind him two dozen local people pick the first grapes of the annual harvest. "Wine is our wealth."

For these workers and the local port wine producers, just like the makers of French champagne, Greek feta cheese or Italy's Parma ham, the EU's name-protection laws help ensure their livelihood by shielding them from industrial-scale, lower-cost copycats.

But port wine's second-largest export market is the United Kingdom, and the impending British exit from the EU is throwing port's almost 50 million euros' (58 million US dollars) worth of annual business there into doubt.

That's because London conspicuously isn't saying whether after leaving the EU next year it will keep the bloc's name protection rules. It could, for example, choose to let in rival port producers from the British Commonwealth, such as South Africa and Australia, as it casts around for post-Brexit trade deals.

Authorities in the United States have long fought against the EU's Geographical Identification (GI) laws, saying they amount to trade barriers - an argument that is not lost on the British government as it eyes closer business ties with Washington.

Product name protection is not a minor issue.

Last week, the EU's Brexit negotiator Michel Barnier singled it out as one of the three main outstanding questions, alongside a possible future border in Ireland and working out the post-Brexit EU-UK relationship.

Enrico Bonadio, Senior Lecturer in intellectual property law at City, University of London, says Geographical Identification laws are "a very sensitive issue which could jeopardize the whole Brexit negotiations."

He reckons the British government, aware that the UK is a major market for the more than 3,000 EU-protected items, is using the issue as "a bargaining chip" to win advantages in other areas of the negotiations.

EU protected names are prized by businesses. The labelling comes with strict regulations on production and is regarded as a quality guarantee that helps branding and sales.

The EU says the scheme seeks to protect local economies and cultures against misuse of names or imitations.

The policy has been a flashpoint before, being a factor in holding up a trade deal between the EU and the United States, where Geographical Identification rules fall under trademark law and where feta and parmesan, for example, are considered generic names.

Portugal's port wine industry offers a look into how a protected name earns its special status and what's at stake for families and businesses in the Brexit talks.

The Douro Valley has an abundance of arresting landscapes along an almost 200-kilometre (120-mile) stretch, reaching from the Atlantic almost into Spain. The spectacular scenery places it on a par with other outstanding European wine regions, such as the Rhine Valley in Germany or France's Loire.

The valley's steep and stony slopes are scored with contours of green vines that ripple back from the river in corrugated lines. Terraces of ancient walls, hand-built in local brown slate, hold gravity at bay. The quiet landscape is punctuated with ridgetop clusters of whitewashed houses and port wine estates called 'quintas.'

Several factors, producers say, make this a singular place: it has weather extremes, with summer bringing heat well above 30 degrees Celsius and winter bringing snow and ice; grape varieties such as Touriga nacional, Tinta roriz and Barroca are unique to Portugal; the poor, bone-dry soil means fewer grapes but a high concentration of sugar; and the slopes, up to 600 metres (2,000 feet) high, offer varying angles of exposure to the sun.

Tractors and trucks have replaced the mules and oxen of yore, but plenty has remained unchanged - including grape-treading in a knee-high granite tank called a 'lagar,' which remains common.

Port is the queen of Portuguese wines. A bottle of 19th-century vintage port, which is the top of the range, can fetch more than 3,000 euros (3,500 US dollars) at auction.

It is a fortified wine, made by adding grape spirit to halt the fermentation and keep the grapes' natural sweetness. It allows wine makers to produce deep, delicately textured wines admired around the world.

It is an ironic twist of Brexit that Britishness runs through the history of Portugal's port wine trade like marbling.

The port business was largely created by, and flourished because of, the British. The port companies, or 'houses,' are called Taylor's, Croft's, Churchill's, Warre's, Sandeman, and Symington, among others.

Taylor's, for example, was established in the Douro Valley in 1744 by Bartholomew Bearsley. After him came, among other bosses, Joseph Taylor, John Fladgate, Frank Yeatman and Alistair Robertson, whose son-in-law Adrian Bridge is now the Managing Director.

Bridge's office is in Vila Nova da Gaia, on the coast by the city of Porto, where the port companies have traditionally brought their wines for aging and shipping.

Standing amid hundreds of centuries-old barrels piled in rows in a musky cellar with granite walls and a wooden roof, Bridge notes that Brexit is already hurting business as the British pound's drop in value against the euro has pushed up port's price on UK shelves.

Taylor's sells port to 105 countries around the world, but Britain is far and away the most important he says, though plans are afoot to expand port's presence in other markets.

He adds, with typical British understatement, that he expects Brexit to "require some degree of readjustment."

Raymond Reynolds, owner of Raymond Reynolds Ltd, a specialist UK Wine importer is not too worried about geographical denominations, which he believes are superceded by historic links between suppliers and buyers.

"They are trusted in terms of their quality and through to retailers and consumers that works as well," he says, adding "the only problem with Brexit is the uncertainty."

Britain and the EU have not yet finalised their divorce agreement, stirring fears among businesses of disruption to trade.