A We've been shown unofficial Nielsen data which seems to go against your suspicions. Since October last year, the average price of a bottle of wine in the off-trade has risen by 15p - that is, from £3.99 to £4.14. But only one of the top-selling brands, Lindemans, has matched that increase. Banrock Station is actually 16p dearer than it was 12 months ago and Jacob's Creek is up 14p, in line with the Chancellor's duty hike.
As for the rest, Echo Falls is up
9p, Gallo by 8p, Blossom Hill by 7p
and Hardys by 3p. Only Wolf Blass, Kumala and Stowells have experienced price reductions, of 16p, 7p and 2p respectively.
There are all sorts of reasons beyond the duty increase for the rising prices, just as there are several causes for a price to fall. In the current climate it's fair to say that retailers are keener on keeping prices down than their suppliers.