Changing your name
As long as you aren't trying to deceive or defraud anyone, you can call yourself any name you choose.
You don't need to follow a formal process in changing your forename or surname. However, all UK government departments (including the Home Office Passport and Identity service), the DVLA and other official bodies won't recognise a name change unless a formal process is followed, so it is usually better to change your name formally. You can do this by statutory declaration or deed poll.
Statutory declaration or deed poll?
If you are using a new name but have never taken any formal steps to change it, or, you now wish to change your name, you can use a 'Statutory declaration' to formally acknowledge your new name. You have to take a statutory declaration to a Commissioner for Oaths, so that it can be formally 'sworn'. This makes it valid. All solicitors are Commissioners for Oaths in Northern Ireland. After this, you keep the document and make copies of it to show proof of the name change when you need to.
Statutory declarations can be cheaper than the deed poll method, but the disadvantage is that some UK government departments and other organisations do not accept them as evidence and ask for a deed poll instead.
A deed poll is the more traditional method of changing your name. It provides official evidence of the change. It needs to be signed by 2 witnesses aged 18 or over (not your spouse, civil partner or anyone living at your address). As an optional extra, deed polls can be for a fee 'enrolled' at the Royal Courts of Justice – this just means that there is a public record of the change. You will need to prepare extra documents to enrol a deed poll and pay to have the change of name advertised in the Belfast Gazette.
Changing a name on your birth certificate
If you are over 18 and your birth was registered in Northern Ireland then you can formally record your name change with the General Register Office Northern Ireland (GRONI). This process results in an amended birth certificate with your new name on it. You have to pay a fee for this process. There is an example form available for this which sets out a Statutory Declaration for you to sign. This declaration must be 'sworn' in front of a Commissioner for Oaths, Justice of the Peace or Lay Magistrate.
To change your forename, you must not have previously changed your forename since turning 18 years old. To change your surname, you must not have a surname change under this procedure in the past 5 years, nor more than 3 such changes since you turned 18.
Changing the name of a child
You may only change the name of a child if you have parental responsibility for that child.
To change the name of a child, the deed poll must be signed by you or another person that has parental responsibility for the child. Every other person with parental responsibility for the child must also consent to the application.
If the minor is 16 or over, they must give their own consent by signing the deed poll in both their old and new names. (Note also that you can't change a name by deed poll for a child over 16 who is or has been married or in a civil partnership. They would have to do their own.)
If your child's birth was registered in Northern Ireland then you can formally record their name change with the General Register Office Northern Ireland (GRONI). This process results in an amended birth certificate with their new name on it. You have to pay a fee for this process. There is an example form available for this which sets out a Statutory Declaration which everyone with parental responsibility must sign. This declaration must be 'sworn' in front of a Commissioner for Oaths, Justice of the Peace or Lay Magistrate. A name can only be recorded as changed once at the GRONI if under the age of 18.
If you wish to change your child's name, but not everyone with parental responsibility consents, then you may apply to the Family Proceedings Courts for a specific issue order. The court can make a declaration as to what the child is to be known as. They can also make a direction for everyone with parental responsibility to attend at GRONI, or sign the necessary statutory declarations to enable an amended birth certificate to be issued.