My partner walked out on me when I was 5 months pregnant and I want the child to have my surname as I already have 2 children with my surname but my ex pazrtner insists she has his surname what rights do I have?

The mother has 100% of the naming rights.

You can name your child anything you want.

If he wants it changed, he needs to take you to court after the child is born and prove that it's in the child's best interest to change it.