a) Your Irish naturalisation certificate
b) Your marriage certificate (apparently it is still required for Irish citizen fathers, but not for British citizen fathers)
c) The child's British birth certificate
d) proof that you were resident in the UK at the time of the child's borth (pay slips, council tax payments, etc).
Passport policy - Imnmigration and Right of Abode wrote:Irish citizens
Irish citizens are not subject to restrictions when they travel to the United Kingdom. In order for their child to gain British nationality, they would have to be considered as resident here in order to fulfil the requirements of the Act.
Irish citizens may be automatically accepted as settled for the purpose of section (1)(1)(b) unless there is clear evidence to the contrary. For example, if staff were advised that the parent was on a short visit to the UK, or that long periods of residence had been spent outside the UK, it would be appropriate to ask the applicant for further clarification.
Following the introduction of the full birth certificate policy, it will now be necessary to be satisfied that the parent is an Irish citizen. In the absence of an Irish passport, the parent’s birth certificate confirming birth in the Irish Republic before 1 Jan 2005 will be required, together with the parents' marriage certificate if status is obtained through the father.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.