The policy on dual clan membership has in the past been unclear. GCHQ have decided that from now on the policy shall be:
"No [SAS] member may also be a member of another clan playing official [SAS] games."
What that means at present is that [SAS] members can't be a member of another clan that plays RvS or SWAT 4.
This will probably be added to the Code of Honor in due course.