My child's birth father is happy with the adoption, so isn't this a formality?

No. The main factor will be whether this proposed adoption would be best for the child concerned. However, there are many factors that have to be assessed, including how adoption will affect other family members, including grandparents, contact issues, inheritance, etc. The Court will want to be assured that adoption is in the best, long-term interests of the child and that any agreement is given freely and with full understanding of the effects of the adoption order.