No, I don't think it's Celtic.
If it is lead then some kind of token similar to this is likely:
https://www.vcoins.com/en/stores/marc_breitsprecher_classical_numismatist/8/product/england_lead_token__cross/1104924/Default.aspx
If it's silver then it could be Anglo-Saxon, as some of those are also similar.
Perhaps someone will come along who recognises it! Fingers cross potented 🤔