Indeed, that's exactly my point. All the comparisons you make are all reduced (genuine reductions), including this one and not at all imaginary as you stated.

Because at £20 it's not competitive with other Champagnes. Morrisons currently have their own label at £15 and Piper-Heidsieck, a major brand at £20. Many supermarkets have - or have had Lanson at £20

The regulations on price reductions require products to have been on sale at the higher price (usually for at least 28 consecutive days). I expect this is what you saw

I've got a spreadsheet of ALL supermarket champagnes here. Shows an easy to compare list.

Your comment bores me, is that ok with yourself ?

Get what you pay for , splash out get a decent bottle of bubbly instead

Vinegar

Save yourselves the hassle and spend the same amount or less on prosecco. Tesco finest prosecco £8 a bottle beats any sub £30 champers. Lovely stuff

Or Aldi Monsigny Champagne at £9.99 without an imaginary price reduction.