The RAF has been expanding its squadron numbers despite the drop off in aircraft numbers for many years now. All OCUs are now given active squadron number, what were training units are now squadrons, UAVs are now assigned squadron numbers, the list goes on and on. 206 Squadron has two aircraft !
As to the P8 being assigned to two squadrons, there are actually three squadrons if you take account of the ISTAR training squadron who are involved.
Jobs for the boys, got to keep those Wg Cdrs employed somehow and when CAS reports to the PM he given out a highly inflated number while puffing out his chest.