If you can, get yourself some Stopham wines whites, the Pinot Gris is excellent, and their Bacchus is pretty good too, as is Nutbounes Bacchus. You can get the Stopham wines in Hennings, and possibly Quaff. Another one I think is pretty good is the Albourne vineyard range. English whites are so...
At least that much is duty, it's higher on stronger wine I think. Once you go over £10 a bottle then the percentage cost of tax on a bottle reduces, but a £5 bottle is typically over 50% tax, e.g., a £6 bottle of 15% red is 52.7% tax, so you're getting £2.84 worth of wine.