If your ex, the father of your children is on a tax avoidance scheme so he pays little to no maintenance in the UK, read on as to what you can do.
Firstly, although tax avoidance schemes are not illegal they have to be used in the way Parliament intended. A tax avoidance scheme is a loophole that these aggressive tax avoidance people use to pay nothing. They usually do this in a few ways, especially if they are Directors of their own company. Look them up on Company House, then firstly, reported to HMRC and AAG for tax avoidance. It's all anonymous. Parliament did not intend them to be able to use this tax loophole.
About child maintenance and how to get all of his income included in the assessment. A variation to the CSA won't change anything. You have to appeal the CSA decision so it goes to the appeals department in the CSA who have more power, and when you do you write this to them:
1. That you have failed to include as (INSERT FATHER'S NAME)income that part which he draws through a loan arrangement and probably via a remuneration trust.
It is my view that these payments either form part of the basic remuneration package and so should be taken into account within the underlying assessment or that they should be brought into account as a variation under regulation 19(4)(a)(ii).
2. That you have failed to take into account as assets in applying Regulation 18 any balance held in his remuneration trust, the value of his shares in his company and the balance on his loan account with his company.
3. That you have failed to take into account under Regulation 19(1A) the dividends received from his company.
4. That you have failed to properly apply Regulation 19(4) to the diversion to (INSERT FATHER'S NAMEE) company by his failure to draw an appropriate salary.
5. That you have failed to properly apply Regulation 20 by your acceptance without supporting evidence that (INSERT FATHER'S NAME) partner pays all their outgoings.
This letter covers all aspects of the aggressive tax avoidance scheme he's on. Also by getting him investigated by HMRC tax avoidance and AAG Aggressive Avoidance Group he may well find himself been investigated for the last 6 years of tax and have a hefty bill to pay to HMRC.
This income will all be used in his child maintenance assessment. If at this stage for some reason the CSA appeal can't do anything, they will send it to Tribunal. You will win the outcome.
I write from experience, didn't have go to Tribunal just CSA assessment and WON.
Good luck and fight for your children's money for their upbringing.