You will need to prove that you have the relevant experience which is 18 months if you want to take eithier the A licence or P licence, if you wish to take both together as most people do you need 30 months combined.
In addition you will need to get authorisation from the FAA to sit the exams, in the UK you have to get a letter from the CAA stating that they have seen & certified you experience then go & meet the FAA who say yes or no.
If you are working at an FAA approved facility that will provide you a letter stating that you require it for your job I think that should be sufficeint but stand to be corrected on that.