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No champagne or prosecco thanks
I had an Oyster Bay one a couple of weeks ago which I thought was very good. £13 I think at Waitrose.
Recaredo always hits the spot with me - much better than a lot of Champagnes. Not sure how available it is over here though.
http://www.wineanorak.com/wineblog/spain/recaredo-world-class-cava
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Friend of mine swears by Cafe De Paris for cava. Personally I prefer a nice Crémant de Bourgogne or a Saumur as an alternative to champers. Much prefer it to the cheap 'real' stuff.
What taste/flavours are you looking for, had so much variation in most things to go by type.
Cordonui (wrong spelling) or Freixnet are both pretty good...dty and crisp.
Aldi do a good one for £4.50.
A good cremant to Limoux is fantastic stuff (as good as many champagnes), but unless you drive down to Carcassonne then you probably won't see it as it seldom appears in UK retailers.
Tescos vintage cava ain't bad