From the website of the British Egg Industry Council:
Q.Where should eggs be stored?
A. For optimum freshness and food safety, eggs should be kept at a constant temperature below 20C. To avoid the typical temperature fluctuations in a domestic kitchen, we recommend that eggs are stored in their box in the fridge
Also:
Q. Why aren’t eggs kept in a fridge in supermarkets?
A. For optimum freshness and food safety, eggs should be kept at a constant temperature below 20C. Most modern supermarkets are kept below 20C so it is not necessary for retailers to store them in a fridge. This also prevents significant temperature fluctuations (for example eggs being moved from a fridge to a hot car after purchase)
Also:
Q. How fresh are the eggs in supermarkets?
A. EU legislation requires that the maximum ‘best-before’ date on eggs must be 28 days from lay. To ensure optimum freshness, Lion eggs have a best-before date of up to 27 days from lay. For Lion eggs this must be shown on the shell (although this is not a legal requirement). Eggs have to be collected from farms at least twice a week and in practice most Lion eggs are delivered to the supermarket within 48 hours of being laid
And:
Q. How can I tell if my egg is fresh?
A. All Lion Quality eggs have a best-before date printed on the shell as well as on the egg box to ensure freshness. One simple test of freshness is to place an egg in water: generally, if the egg is stale it will float and, if it sinks, it is fresh. This is because as the egg gets older, the size of the air sac increases, making it float.
Source:
http://www.egginfo.co.uk/faqs
Chris