The code stamped on every UK egg isn't a marketing invention or something a supermarket dreamed up -- it comes from law, and it's been there for a couple of decades.
An EU rule from 2004
The current stamping system was introduced across the EU in 2004, as part of a wider set of rules on hen welfare (Directive 1999/74/EC). The idea was simple: give every egg a code that says how it was farmed and roughly where it came from, so the information travels with the egg all the way to the shelf.
That's the same first-digit system EggTracker reads today: 0 for organic, 1 for free-range, 2 for barn, 3 for cage, followed by a country code and a producer ID.
What happened after Brexit
When the UK left the EU, it didn't scrap these rules and start again -- it kept them as what's sometimes called "assimilated law", carried over largely unchanged. The main practical difference is who enforces it: UK bodies like the Animal and Plant Health Agency and Defra now oversee it directly, rather than the EU.
The upshot for anyone using this site: a UK egg code today means exactly what it meant before Brexit, and exactly what the equivalent code means on an egg bought anywhere else in the EU.
Is EggTracker part of any of this?
No. We're not a government body, a regulator, or affiliated with the scheme in any way -- we just read the code that's already printed on your egg by law, and estimate a distance from it. See our FAQ for more on how the tool itself works.
Curious what the code actually decodes to? See What are the codes on eggs?
Sources: Wikipedia -- Egg marking; pid-labelling.co.uk.