Not really. All you need to do is try before you buy. And if you can't it doesn't mean there will be a problem. Lidl in the UK used to stock a Greek olive oil (we are discussing EVOO, so I won't keep repeating it, all else is suitable for engines, not humans), which I bought once when I ran out and it was very good (the more expensive one, they also have a cheaper Greek olive oil, too, but I haven't tried it).
A friend bought Sainsbury's own brand Greek EVOO and it tasted bitter. Very bitter. We threw it away. I think it must have been stored badly. Or anyway, something had happened to it. And I have seen bottles of olive oil on sunny shelves in British supermarkets and crionged. Olive oil should be kept in a dark place, otherwise it becomes rancid. And I think that bad storage is a very common problem in the UK and you can see olive oil that has changed colour due to bad storage being on the shelves and sold to people who know nothing about it.
So first of all look for a dark green glass bottle or a tin. Not a transparent bottle. If you buy a tin, then decant it into a glass bottle once opened. At home store your bottle in a dark place (and the bottle you decant it into does not have to be dark, since it is kept in a dark place).
Then, first of all avoid Elais (owned by Unilever) and their engine oils. They may be big, very big, but I don't know anybody who buys their stuff in Greece. Maybe people who know nothing of good olive oil (unlike their long-running tv ad that goes "I am from X and I know how to distinguish good olive oil" where X is some olive oil producing region, είμαι από την Καλαμάτα και ξέρω να ξεχωρίζω το καλό λάδι etc etc).
Then avoid supermarket own brands unless you are certain that they have been stored appropriately. Lidl stores them appropriately, Waitrose does not. I have seen many bottles enjoying the sunshine in Waitrose shelves.
Then go for one of the brands mentioned here. Kolymvari Gold is a very good combination of price and taste and widely available in the UK. Bevellini, from the same people who import Kolymvari Gold is probably very similar.
A few years ago Sainsbury's used to stock Greek Artisans Early Harvest, and I think it is the best bought olive oil I have ever tasted.
Other than that, remember that price does not mean quality. In Greece almost everyone has some source of own olive oil, and many have turned to putting it in fancy bottles with designer logos, giving it fancy ancient sounding names and trying to sell it overseas for extortionate prices. Most of the olive oil they bottle and sell comes from the same trees and producers as the one not sold in fancy bottles with fancy names. I think I know the one Daeman talks about, it was on sale at Selfridges for £45 a few years ago. The USP was that it was filtered. Like 99.9% of all olive oils. Nice fancy bottle but someone who tried it told me it was nothing special. This stuff is aimed at those who know nothing about olive oil but want to show off their expensive and refined tastes. There's even
a shop in London owned by Greeks, who sells exactly that: the dream, the idea that olive oil is a hip, gourmet product for people with money. Pretty much the same snobbishness the UK public have with wine, which they drink neat (horror of horrors) and they pretend they know about it (another horror). And the same thing that is happening with coffee and hipsters (and ridiculed in a very funny Macdonalds ad recently).
I am not saying that it is not good, I am saying that it is not good value, because what costs about 3-4 euros wholesale is sold for 20-30 once inside the fancy bottle. Also, I don't mind that the shop sells what it sells There is market for that, and they cater for that market. But for most of us, who have access to plenty of olive oil from our own trees this type of commercialisation is a source of amusement. So buy whatever you like, but don't pay £10 for 250ml. Even if they promise you it's amazing etc etc. Try it. If you think it is amazing, fine, if not...