Hello y2richie,
I am a British citizen and recently gained Irish citizenship myself through foreign birth registration and can give you a couple of tips.
I cannot guarantee the correctness of my advice - I am not an expert, nor am I a lawyer, but as I said I have been through this process myself, and can give you some advice based on my own experience and understanding. The information you have been provided with so far in this thread by benifa is correct.
To be on the safe side and to avoid any worries, you should double-check everything with the relevant authorities rather than just taking peoples' advice online.
Firstly, on the subject of your gran's birth certificate, do you have the original (or a certified copy) of your gran's Northern Ireland birth certificate? Is it the long form birth certificate (should have her parents' details on it)? If so, then I think you don't need to send off for it, it should be acceptable to the Irish authorities. It must be the original (or certified copy) long form certificate.
You should phone your Irish embassy or nearest consulate where you live (if you're not living in Ireland yet), let them know who you are and that you want to apply for FBR, and let them send you the application forms (I know they are online anyway, but there's no harm in letting them send you information in the post).
Also ask them which authority (Irish or British) will hold your gran's 1923 long-form birth certificate (actually, if you already have a short or long-form birth certificate for her, it should be clear from the birth certificate whether it's Irish or British), so that you can send off to the correct GRO office for it if you don't already have it (the long form certificate I mean), or if you don't want to use your gran's original certificate.
For certified copies of long-form birth and marriage certificates you can use
www.groireland.ie www.gro.gov.uk and
www.groni.gov.uk
EDIT: In fact I just did a quick check and found this out:
From
http://www.groni.gov.uk/what-information-held -
"Births registered in Northern Ireland from 1 January 1864."
And from
http://www.groireland.ie/faqs.htm#37 :
Question: "I want a Northern Irish Birth/Death/Marriage Certificate for the period after 1921, where can I get it?"
Answer: "General Register Office, Oxford House, 49/55 Chichester St. , Belfast BT1 4HL, Northern Ireland , email:
gro.nisra@dfpni.gov.uk"
i.e.
http://www.groni.gov.uk has your gran's birth certificate.
Secondly, as far as losing British nationality is concerned - does it say "British Citizen" in your passport? If so, and you have been a British citizen from birth, then you will definitely not lose your British citizenship, and there is no need to tell the British authorities upon gaining a new nationality. I think it's only certain "British subjects" and "British protected persons" who can lose British nationality in this way.
Take a look at this:
http://en.wikipedia.org/wiki/British_na ... itizenship
And this:
http://ukba.homeoffice.gov.uk/britishci ... tionality/
Also contact the British authorities and double-check your questions regarding dual nationality with them.
e.g. you could phone the Home Office Nationality Customer Contact Centre on 0845 010 5200
http://ukba.homeoffice.gov.uk/britishci ... p/contact/
They will most likely tell you that Britain allows dual nationality, and that there's nothing you need to do as far as the British authorities are concerned. Although on the UK passport application form you are supposed to tell them about all passports you have previously had, and my understanding is that this includes foreign passports, but I haven't had that confirmed yet. You may want to renew your UK passport before you get an Irish one if that turns out to be the case. It wouldn't prevent you renewing your UK passport anyway, so it's not actually a problem, but the British authorities would then know that you have Irish citizenship (which again, isn't actually a problem).
As far as the Irish authorities are concerned, they don't ask new citizens to renounce previous citizenships upon becoming Irish. They also don't tell anyone you have become an Irish citizen. They will know you're British because you're probably going to have to send them a photocopy of your current UK passport with your application.
Sorry if my reply was a bit long, but I hope I was able to help you.
Good luck!
el_gringo
