CMS halved child support BIL pays, he is self employed and fiddling his taxes, can anything be done

[Belleende]

Sister had divorce settled a year ago. Agreed maintenance for kids. One year on ex BIL has wasted no time to apply to CMS to have this reassessed. Amount to pay has almost been halved. He is now to pay less than £150 per month per child, despite probably earning in excess of £60k gross.

He is of course self employed, and is very careful to ensure that his net earnings fall below the higher tax bracket. He does this by massively inflating expenses, and he also earns in another country and does not mention this income.

So, does she just have to swallow this, knowing that he can lie, pay less tax and less child maintenance, meaning she will have to reapply for tax credits (i.e. the British taxpayer ends up paying for his children as he won't). Is there anything she can do?

I’d report him to HMRC.

She can produce the evidence she has and apply for a variation/reassessment. Will probably end up in a tribunal. Have a look here under the heading “Appeals”. www.gov.uk/child-maintenance/complaints-and-appeals

It's getting the evidence that is the issue. Can she get him audited?

No she won’t be able to get him audited, but she’ll have evidence from the divorce of historic earnings, and the tribunal can order him to produce more up to date documents.

He has been fiddling his taxes forever, so there is no change in pattern.

Its going to bite her then as she obviously had no issue with him doing this when together as she benefited but now is missing out so it's suddenly not ok?

She doesn't have to rely on tax payers, she could always support them herself.

Of course he should be paying the correct tax and child support just as she should be financially supporting them.

She does support them and has worked incredibly hard to do so, but as his career has unpredictable and unsociable hours she was a sahm for years and her career and earning power suffered as a result.
They also moved to London for his career. They had a deal, he had five years to make the most of his career and she would focus on the kids, then it would be her time. You can guess what happened then.