Could I enter as a Visitor on my USA passport and provide the FBR Certificate and USA Passport to my employer for the right to work checks?
I would apply for an Irish Passport in London, since the turnaround time is 10 working days. Current processing times are 10 weeks in the USA.
9. A birth or adoption certificate issued in the Channel Islands, the Isle of Man or Ireland, together with an official document giving the person’s permanent National Insurance number and their name issued by a Government agency or a previous employer.
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https://www.gov.uk/government/uploads/s ... orking.pdf