If Britain leaves the EU on March 29 with a so-called hard Brexit, many supporters will likely be celebrating with Union Jack flags and countless bottles of Prosecco.

But worried winemakers in Italy fear potential new trade tariffs would put a huge dent in a market which sees a whopping 120 million bottles of Prosecco exported to the UK each year.

"There could be price rises," said Mattia Mattiuzzo, vice-president of regional farmers' union Coldiretti.

"Without a deal it will perhaps be difficult to find a placement for the product."

The UK is the Italian fizz’s top market.

Brits guzzle down 35 per cent of exports of the sparkling white wine, made in the Veneto region of northeastern Italy with the DOC label, as well as the superior DOCG category.

But as it becomes increasingly clear that British Prime Minister Theresa May's withdrawal deal will not pass, the odds of a no-deal hard Brexit appear greater, along with all the trade uncertainty that would bring.

"It could create discontent among English consumers, as it could create economic difficulties for us to reach the English market," said Mattiuzzo, while gently pruning his family's snaking, dark vines in preparation for this year's grapes.

In 2016, then British foreign minister Boris Johnson caused a diplomatic spat with Italy after apparently suggesting it should back his version of a Brexit deal or face losing Prosecco sales.

The threat was rebuffed by Italy's then economic development minister, Carlo Calenda, who said Britain could then miss out on "fish and chips" exports to the other 27 EU countries.

Italian producers say importers have been stockpiling Prosecco in the UK and in Ireland, where there may be a "backstop" entrance for their wine, amid fears of increased import duties and long queues of trucks at the UK border.

'Globalised world'

"This situation of uncertainty worries us, (but) we're confident that English citizens won't give up this pleasure," said Innocente Nardi, head of the Conegliano Valdobbiadene DOCG Prosecco consortium, standing among dramatic, vine-draped hillsides.

"The main producers are in talks with English importers to set up import places in Ireland for instance, or English-registered companies which can easily import wine," said Nardi.

"In the worst-case scenario, they should still be able to import," he said in the dwindling grey of the northern Italian twilight. 

And if UK-bound exports falter for whatever reason, there are always other markets, said Nardi.

President of the Producers’ Consortium for Conegliano Valdobbiadene Prosecco DOCG, Innocente Nardi.

"At the moment we’re expanding and being appreciated in a significant way in the United States of America, which is an enormous market in which we’re investing, and Canada and Russia," he said.

The wine is named after the nearby village of Prosecco, a Slovene word meaning "path cut through the woods". 

The grapes used to make the wine were also called Prosecco until growers had the name changed to Glera in 2009, so that they could protect their increasingly popular brand as a geographical location.

Although many winemakers are worried, some believe Prosecco sales can withstand Brexit - whatever the outcome.

"I'm very optimistic, I think little will change, because now the world is globalised," said winemaker Angelo Facchin, surrounded by the vast silver tanks where the wine is fermented in San Polo di Piave.

"Prosecco is now part of English culture. As a result, it will be difficult for them to give up our Prosecco," smiled Facchin, whose family has made wine since 1870.

The wine is "not very alcoholic, or expensive, can be drunk at any occasion and be a replacement for beer," Facchin added.

The DOC consortium has also invested in promoting the wine, including by sponsoring the Superbike World Championship.

Britain now accounts for 40 per cent of Facchin's turnover, having expanded by 15 to 20 per cent each of the last five years. 

His wine is drunk at St John's College, Cambridge University, he proudly says.

While some are optimistic, Stefano Zanette, head of the Prosecco DOC consortium, said a hard Brexit would be a "leap into the unknown".

While not wanting to get involved in British politics, Zanette said he supported the idea of a second referendum in the UK on its relationship with the EU.

"Most people didn't realise the consequences of their choice," he said.