For SAS captains on base doing paperwork, the usual expectation is a service/work dress or other authorized day uniform, not combat kit. Exact details depend on the unit, duty, and local dress rules, but for administrative work it is typically a neat office-appropriate military uniform, with beret or headgear as directed and no field gear. Publicly available dress guidance from military forces generally shows that paperwork and office duties are handled in standard service dress or working dress rather than operational clothing.

A practical way to think about it is:

  • Paperwork/day office tasks: service dress or working dress.
  • Operational tasks/drills: combat uniform or mission-specific clothing.
  • Formal occasions: dress uniform or ceremonial attire.

For SAS specifically, public discussion online is often vague and sometimes unreliable, so the safest answer is that they would wear whatever the unit’s dress instruction requires for a base office setting, which is usually a tidy service uniform rather than something tactical.

If you want, I can turn this into a short forum-style answer or a cleaner FAQ- style response.