i have a headcanon that k unit were never actually sas
alex was sent to brecon beacons, not for any kind of training, but to test his endurance and mental strength. in sas, the soldiers are all already trained and have been in the army for at least three years. they are at the peak of their military careers. they know all the basics there is to know.
there was no doubt that alex had the physical aptitude to be a spy, but dealing with espionage when youre under insane mental pressure with nobody to support you—people bullying you and degrading you even—is a whole other level. in addition to being blackmailed into the whole thing. would he spill classified information? that was what k unit was there to find out.
in addition, there is no way ben daniels could have gone from an sas recruit to senior mi6 agent in like,,, 2 day in order for him to meet alex again in snakehead (ahorz timelines really leave much to be desired😭)
k unit may have been in the army once, even the sas at one point, but they all found their way to military intelligence eventually and were sent to see if alex was up for the task
