Difference from Champagne
Champagne is sparkling wines made exclusively in the Champagne region of France.
Sparkling wines made outside the Champagne region cannot be called champagne. In addition champagne must be produced in compliance with the strict standards of the French AOC (Appellation d'Origine Controlee) which regulates permitted grape varieties, yields, production methods, etc.
English sparkling wines are made from champagne varieties* and produced in the same method as champagne. In the UK PDO (Protected Designation of Origin) is applied to English or Walsh wines, however, this is much relaxed requirements for wine producers to comply compared to the French AOC. It is because the modern winemaking is still a new industry in the UK which has started since 1990 and PDO for English wines was only recently established in 2007.Under PDO regulations the UK wine producers can have more freedom and take on a wider range of challenges In winemaking in comparison to European counterparts.
In fact England is geographically in the old world but European new world in winemaking.
* Champagne varieties: Chardonnay, Pinot Noir, Pinot Meunier
Note: In 2021, the Sussex PDO, the first PDO to be granted to a county in the UK, was approved. To this end, wines produced in both East and West Sussex from grapes harvested in Sussex can be labelled with the "Sussex PDO".
It is a little bit controversial, because some of the well-known wineries in the UK have vineyards in a few different regions in the southeast of England. Also consumers may not always have a benefit from the Sussex PDO labelling if it affects to the price of wine... etc.
Anyway it is interesting to see how this PDO is going to be in the future.