Nonsense. You have conflated the use of a word you do not like (attempting, weakly, to substitute a word that is missing too many salient elements) with a grammatical issue (adv. vs noun). Enough.
I would say the opposite, but it really depends on which UK sparklers are imported and available vs. the literal sea of Champagne imported. Generally I would spend less than ½ for a UK méthode champenoise wine.
There are a couple of different bottlings. Assume you mean Ancien Nouveau, but whereas for US import there is an allowed range, we have to report the exact ABV. That is why the labels are often different.