I really do think that it is the personal preference of the midwife. I suspect as a newly qualified I will be encouraged to have a 2nd present. Not all midwives do though. So it can't be policy iyswim. The main mentor that I had for the first 18 months liked to have a second midwife and would buzz for one, after a while I became her second. The last mentor that I worked with said she didn't normally call for a second unless she was anticipating a problem.