If the Army adopted the EM-2, would the Royal Navy and RAF use it as well?
Short answerProbably, because both services normally standardize on the Army's rifle for procurement and logistical reasons.
NotesA British EM-2 or similar Army weapon would likely spread to the other services through common procurement. The Royal Navy and RAF buy too few rifles to make a separate design, ammunition stream, training system, and maintenance chain economical. The later SA80 provides an example of logistical standardization outweighing service-specific preference.