I'm probably going to get this wrong, but I believe that something like £4.00 out of every £5.00 bottle of wine in the UK is tax, so if you buy a £5.00 bottle of wine, the bottle only cost £1.00 to make and transport etc. Therefore, if you buy a £6.00 bottle of wine, the wine itself should be twice as good.
This was all explained by Alan Davis on an episode of QI, but I'm struggling to find the video of it!
Either way, I'm off to find some now...