Taxcheck90

Hi I am a British citizen and have been living outside of the UK for 2 years. I am no longer a UK tax resident. I am starting a new role for a UK company (employee) in January, and will be paid on their UK payroll. As I will be a tax resident in Ireland, and my income tax will be due there, can I apply for a NT code using a P85 now? Also, what are the Employer responsibilites in relation to NI? How is this paid.