Well, I had a trawl.
As ever with Defra, the info is opaque, muddled, knitted across Defra, Business Link, Directgov and other websites, largely unfathomable and generally lacking in any useful detail.
However, as far as I can tell, the regs seem to have moved on since Katie Thear wrote in her excellent book Free-Range Poultry that we must not sell fertilised eggs for eating.
There is a lot of stuff about Class A eggs, which is what I think you need to be able to classify your eggs as if you are selling eating eggs formally in any way
other than directly to the consumer. And maybe if you have more than 350 laying hens too. If in doubt, please do your own research!
Even for Class A classification, there is nothing much to be found about fertilised or not. Just above where it says 'no foreign bodies', it says 'imperceptible germ'. I imagine they mean 'germ' as in embryo, and not 'germ' as in bacterium or other disease-inducing body! So I conclude this phrase means that no-one could detect the embryo. It also stipulates that the eggs must be offered for sale no more than 21 days after laying; in order to use the phrase 'Extra' or 'Extra Fresh', this reduces to 4 days after laying, or possibly 9 but you must read it yourself if this will matter to you.
The document with the most detail in is this one:
http://adlib.everysite.co.uk/resources/000/264/132/EMR1.pdf as of 18th Dec 2011 - please start your own adventure game of Seeking Egg Marketing Rules through the Defra World of Opacity and Obfuscation if you are reading this after 19th Dec 2011.
I nominate myself for the Accidental Smallholder Selfless Action Award for December.
