Some “pay up”. But per my post what they are required to pay is also vastly insufficient to cover their liability for 50% of the cost of providing for the child in terms of housing, childcare and everything else they need. It is calculated as a percentage of the non-resident/ absent parent’s income (and reduced if they decide the have further children or move in with someone with existing children of their own!). That is nonsensical: the cost of raising the child remains the same. They created the child so should pay 50% of the cost. The resident parent doesn’t get to decide not to pay for the child’s clothes or house or food or childcare because they had a drop in income etc. so in effect they have to not only do most of the parenting and all of the career damage that entails but also subsidise the non-resident parent’s 50% of the costs.
The amounts that are required to be paid need to be far higher and based on evidenced cost, not salary. Like all other parents non-resident parents will just have to be poorer themselves and pay for the child’s needs first. Liability for non-payment needs to be made criminal, not civil. The money should be paid to the resident parent by HMRC and recouped from the non-resident parent with the same vigour as non-payment of tax with criminal charges, removal of any entitlement to state benefits at all for perpetrators until they clear the debt in full, and like other countries confiscate their passports and driving licences and register CCJs against their name etc for non-payment: a functional system with enforcement like in most developed countries.
Until such enforcement takes place there is absolutely no argument whatsoever to suggest including money that may/ may not be received (and the CMS often “write off” without the permission of the person it is owed to and receipt of which could cease at any point) in any calculation of income for tax or benefit purposes. Note also that any child maintenance that is received was already taxed before the non-resident parent paid it so trying to include this in taxable income for the other parent who administers it towards the child’s costs which they pay as the resident parent (it isn’t for them, but the children) would mean double taxation.
Your comments and those of @BigAnneseem to be an attempt to demonise single parents who are doing the work of two people already and are the responsible parent who has remained and actually fulfilling their responsibilities. It is quite disgusting to be attacking them, of all people.
As an economist I can tell you with no doubt at all that the problems with the UK economy are absolutely nothing to do with single parents. This is just nasty, spiteful rhetoric with no basis in reality, I’m afraid.
In short, you are barking up the wrong tree and this has pretty much zero impact on the issues with the UK economy, although the utter failure to provide robust enforcement does of course impact single parent families very negatively, who are already penalised significantly by the UK tax system, compounding existing disadvantage.
I suggest you find a new hobby horse.