I've recently had dealings with the CMS since divorce finalised. Domestic abuse. Father left in first trimester. Never supported child: always agreed to but used it as blackmail. Women's aid advised, because of the continued and escalated level of abuse, to not pursue maintenance until divorce finalised. My sons second birthday was 2 days ago and we are 2 maintenance payments down the line...
This is as a direct result of the Child Maintenance Service (new CSA) and their policies including this percentage system. Yes there are flaws that could be detrimental for families but my experience has been very positive.
From my experience I have learned that from the date I opened a case with them, any missing payments can be recovered. Any from before that time they cannot. So father remains liable for that. It works via NI and HMRC which leaves loopholes for self employed and company owners/directors who have HR type swing, yes, but not for the average joe. I do not / will not have to pay a percentage unless they have to intervene when father misses payments but the threat of the 20% bump up to his payments if they have to extract the money from his bank account, as well as the added percentage if they have to go to his employer to take it at source changed his mind. My opinion was that my 4% loss of the maintenance I have never received was better than the absolute nothing I was getting. The hilarious part was that he spent a fortune on a lawyer to fight the CMS and the harassment case he was trying to go forward with for them hounding him only to be told that he had no choice - the amount wasn't a guideline and he was liable for every penny. Obviously did not go to court and he conceded to pay the stipulated amount in full every month and without the need for them taking action.
For me the threat held quite a lot of weight and got results. It's like a built in fine. If the father is absolutely determined to go the long haul in obstructing the CMS it can take up to 6 months for them to recover all the money which is another pitfall for struggling families but the entire amount can be recovered in so many ways - debt collector fashion, but that only helps if you're financially able to wait for it
This is my experience though... Not suitable for all