This page from the Royal Aeronautical Society the professional body representing the aircraft industry in the UK might shed a little light.
www.raes.org.uk/cms/uploaded/files/GCAA1.pdf
So if I want an Eng after my name all I have to do is apply for it.
Reminds me of that old BT advert with " Beattie" gassing on the phone about her son
"he's got an 'ology" !!!!!!!!!!!!!!!!!!!