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
Take a look at http://www.wineanorak.com/ I really enjoy his approach to wine writing and there are some good recommendations. Alternatively go to Majestic or a good local merchant and tell them what you like and let them recommend something for you. We have the Wine House...