Dont quote me either, but I think you can start as soon as you like.
But..... that will affect the date when you have to go back.
ie. if you have a 12 month leave period, and you leave 3 months before your due date, you will be expected back when bubs is 9 months old.

I know girls who have finished work as early as 28 weeks.
I finished at 32w with DD and it wasnt questioned at all.

Good luck!