About 2/3years ago. Same cleaners but different uniforms. I believe kings x cleaners are still in house but everywhere else is agency-initial I believe. Welwyn train cleaners (station not yard) used to be FCC employees, a couple of years back they became initial.
I can tell you that at the time of the TSGN bid there was no major change in the way cleaning had been done since the start of the franchise, i.e. they made use of agency staff to cover vacancy gaps, apart from Brighton (where Southern had previously performed the cleaning). Said vacancy gap was certainly bigger than it needed to be, but no staff were made redundant AFAIK.