Bought this tonight for £3.36 per bottle plus an extra 5% off when you buy six bottles.
This was for their own brand Demi-Sec which some call medium dry and is actually a lot easier to drink than the Brut variety which is Dry.
Its shows up online as also being on offer but says "not in stock" when you try the website. Although the regular Brut is in stock (online) but strangely was not on offer in store.
This is basically 25% off what I feel is a good value wine to start with, no where near as nice as the M&S version, but they sell theirs at £8 where as this normally sells at £4.49 and if put in the freezer for an hour to chill down, really improves. :)
Hope its of help to someone.