With A and E in England, I am not sure if you have also completed a pediatric and maternal care rotation. I know that they do things differently in the UK, you are either an adult nurse or a peds nurse. For the US you are required to have training in all of the areas. If you do not have the hours they will need to be completed in an approved school of nursing before CGFNS will allow you to take the exam.
You must also complete the Visa Screen process, this is separate from the CGFNS exam part.
To take NCLEX exam, you will need to apply first to the Board of Nursing (BON) for the state that you want and be evaluated by them. If approved, they will send you a letter "ATT" (Authority to test). Wait until you have this letter in hand before paying and scheduling your NCLEX exam.
I made this more detailed than you may need since I keep getting requests for this info. This can also help someone else.
Good luck..................wish you much success