If you're not too confident on wine then use the wotwine? app. it's free. All the supermarket wines have been tasted by professionals (master of wines, sommeliers and stuff) and you just scan the bar code and it will tell you if the wine is really good and worth the money. Or you can search by your favourite supermarket, wine style and price band. Simples!
DON'T buy on promotion! if you have seen the WHICH? report those are all artificially inflated prices just to reduce the price and they are rarely even worth the reduced price. It's a big scam!