21 SAS vs 23 SAS vs 22 SAS
22 SAS is the regular, full-time SAS regiment. 21 SAS and 23 SAS are reserve regiments whose members keep civilian careers and train alongside them. All three form part of United Kingdom Special Forces; the practical difference for anyone applying is full-time service versus reserve service.
22 SAS
The regular regiment, based in Herefordshire. Soldiers serving in 22 SAS do it as their full-time job, and the usual route in is from an existing career in the regular Army rather than from civilian life.
21 SAS and 23 SAS
The two reserve regiments. Members are civilians with ordinary jobs who train in their own time and attend selection alongside that. They are recruited regionally, which is the main practical difference between the two for an applicant: where you live tends to determine which one you approach.
What is the same
The demands are not softened because you have a day job. What I saw at the assessment stage was a process entirely uninterested in how busy your week is — you either arrive prepared or you do not, and most people who struggled had underestimated the preparation rather than the day.
Which should you apply to?
If you want to serve full-time, that is a regular Army route. If you want to attempt this while keeping your career, the reserve regiments are the ones to talk to — start by contacting the unit covering your area.
A note on accuracy
Entry criteria, standards and selection dates are set by the Army and change over time. Take anything current from the Army's own UK Special Forces Reserve pages; take everything below as one applicant's experience.
Get my 21 SAS reserve selection prep guide
What the stages are, what I was training to before I applied, and how I'd build the twelve weeks before a selection weekend. Written from my own application, free, no pitch.