From a personal perspective, I also agree that his ex's partner's financial circumstance and whether the father has access or not has no bearing on child support. You are required to pay it by law.

I am the payer. My XH is the payee. The child support arrangement is between him and me, not us and our partners. My new partner's income doesn't get taken into account (which would most definitely increase child support in my XH's favour) so I don't expect my XH's new partner's financial circumstances (should he get one) to favour me.

However if he was receiving new income (like rent on a home he owns), that would change his income, so I (and your dp) could ask for a new assessment based on that. If she owns the home clear of any mortgage, almost the entire rent she receives would be considered income.

And the reason the CSA have power to garnish wages, take money from accounts etc is because it is not a choice for the payer not to pay the payee. Or else everyone would have some sob story about why they shouldn't pay.

And access to child is not tied to child support because that way, a parent can't threaten to with-hold access to a child to get more money. And similarly, a parent can't withhold money to get more access to a child. Child support is making both parents accountable for the financial upkeep of the child in the fairest way possible.

The CSA have to balance the needs of the child and to be honest I think they do it well in most cases. And I think in most circumstances child support doesn't even touch the sides of what it costs the primary caregiver to properly raise a child. Which is why I chose to pay more than what I'm assessed at. Because you don't stop being a parent just because you don't get to see the child. And the money you pay is your contribution to that child, irregardless of what you think of the other parent.

So I'm personally all for garnishing wages and taking money out of the parent who is in arrears. Because it's the fairest system for everyone, and stops people from avoiding their responsibilities.