EDIT: Finally found the SI : https://www.irishstatutebook.ie/eli/...62/made/en/pdf . This was made 3rd Dec, not sure how I missed it (or maybe it wasn't actually published when I looked)

Interestingly it says "no more than 48 hours prior to the date on which the person arrives in the State", but then it says "no more than 48 hours before the person
arrives in the State", so there's some nice consistency...

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I've looked through a fair few SIs and laws and I can't find any reference to antigen tests being permitted or any reference to 48 hours. Perhaps I'm not looking hard enough. What's weirder is I can only find references to PCR tests, so the legal state of affairs might be a more strict test needed under law whereas the Government is merely giving 'guidance' that antigen is acceptable

I find it particularly fishy that there is no clarification about what proof is needed, exactly what a supervised antigen test means etc.