I transferred into an office , at the time I was part time,(but I had been F/T for 12yrs) but my senority was taken with me, then I had done 16yrs so I went from 48 on the list in my old office to 13 in the new office, as it was a smaller office,
So that should answer the question, just clocked up 20yrs and no way should seniority be stopped
Essex mum
