Having now found this, would like to comment on a few points upthread.
''Never give misery an even break, nor bad wine a second sip...'' from the late Greg Trott of Wirra Wirra, a character and visionary down under. Fortunately, we have very little bad wine now in the UK, but we have a huge amount of mediocre wine, mostly in supermarkets. However, it was the supermarkets that led us to more choice and less bad wine, which was good as everybody upped their game. Nowadays, decent wine can be found in the supermarkets, it is just the hit rate is not as good as a local wine merchant (LWM). They are also notorious for their hi-lo policies - list at a higher price so a 'discount' can be shown. The discounted price is usually the 'true' price.
Avoid the bottom shelf - you are paying far too much tax compared with whats in the bottle.
Avoid stuff labelled British wine - it is certainly not british and barely qualifies as wine.
Value can be found in their higher priced Own Label ranges e.g. Taste the Difference at Sainsburys, Tesco Finest etc. Also, the Co-op tends to fly under the radar; it has good buyers and in the larger stores offer a good selection.
The Wine Society - is probably the UK's best overall merchant, providing excellent value to quality ratio, after you forget about their joining fee. Reason is being member owned, they do not have to make a profit. However, I do tire of their overbearing marketing. I also think their range is too big; e.g. right now they have 21 ozzie chardonnays and 25 kiwi savvy b's. And very occasionally they are more expensive e.g. an absolute bargain I have bought is Biferno Rosso, now 9 quid and only 8 quid (or less) at the Co-op.
Naked Wines - not a huge fan. Some of their stuff is good, much is overpriced. Unless you're an Angel.
Sunday Times Wine Club - is Laithwaites by another name. As is the British Airways club. The worlds largest mail order wine company and hugely successful. But their bombardment of mail, emails, phone calls is relentless. Some stuff is good and can be excellent value but it can then disappear from their lists. Overall, extremely irritating for me.