Didn't Britannia play host to vineyards during the Empire? I think we have some nowadays, come to think of it.
The Champagne region of France is a particularly good region to grow wine due to the chalk (calcium carbonate) which is present in its subsoil, which gives the wine its trademark lightness. As global warming changes climates, the location of where there will be optimal climate conditions for the growth champagne will shift northward, towards Britain.
Kent, home of the White Cliffs of Dover (which owe their whiteness to chalk), is becoming the ideal place for wine vineyards which produce champagne. So, perhaps one ought write a timeline, either in a warmer future or during a warmer time of human past, where OTL's Champagne is known as Kent.