I enjoy a drop of red but im by no means a expert . As the saying goes " a good bottle of wine is one you enjoy " I really like the zenith ( kumala ) one atm which is about £10 a bottle can can be got for a fiver now and then it is very moorish . Palace co chairman steve browett owns farr vintners and has a wine thread on the bbs where he answers all wine queries which is quite enlightening , if you dare to cross over .
Maybe £5 is actually nearer the value of this wine. I am not knocking it if you find a cheap plonk you enjoy, then go for it, but don't kid yourself they are doing you a favour selling it at half price.
http://www.bbc.co.uk/programmes/b006mg74/features/supermarket-wine-oz-clarke