The withdrawal agreement ties Britain into respecting EU laws, and adopting any new ones. This covers food safety and the environment to protecting food labels during a transition period. And the other 27 governments want those rules respected far beyond that, to stop Britain undercutting their own producers. Elena Casas reports from Champagne - where winemakers are very keen that Britain continues to play by the EU's rules.

Charles Fourny has run the Veuve Fourny et Fils champagne house with his brother for 25 years - 80 percent of their bubbles are exported, much of it across the Channel.

CHARLES FOURNY CHAMPAGNE PRODUCER "We are a small producer, and there are a lot of British wine lovers who really appreciate what we do, so it is important."

For champagne producers, Britain is by far the biggest export market.

ELENA CASAS EPERNAY, FRANCE "It was the British love of bubbles that led winemakers here to develop what's now called champagne two hundred years ago - and in 2017, 27 million bottles of it were exported across the Channel. But that's 8 percent down on the year before - a drop blamed on the fall in the pound."

Charles Fourny says he's not too worried.

CHARLES FOURNY CHAMPAGNE PRODUCER "Champagne is one of the great pleasures of life, so it's not too affected by a price rise. The British have a deeper relationship with champagne than that."

But exporters do fear the volatile exchange rate and a weak British economy after Brexit might mean British buyers just can't afford so much bubbly. Their other concern is regulation - after Brexit, Britain won't necessarily have to stick to EU rules on protected food labelling, meaning there would be nothing to stop English sparkling wine producers labelling their product champagne.

THIBAUT LE MAILLOUX INTERPROFESSIONAL COMMITTEE OF WINES OF CHAMPAGNE "Champagne is the name of champagne and not of other sparkling wine, we cannot move Champagne to other places, the champagne concept relies on the link between the geographical denomination, the area, and certain production rules, and this makes the quality which is particular to champagne."

The French government says it won't sign up to any deal that doesn't guarantee protections for its gourmet products. France is also the key voice insisting Britain be forced to stick to EU rules on everything from workers' rights to carbon emissions cuts as part of any future trade relationship, to prevent British businesses undercutting their continental counterparts. For many Brexit-supporting politicians, cutting so-called red tape is why they wanted to leave the EU in the first place - meaning the months of talks needed to get this withdrawal agreement on the table are likely to be just an aperitif for the arguments over the future trade deal. Elena Casas, Epernay, France.