First time I have involved them since we split, exH has always paid the amount we agreed between us (although it hasn't gone up in the last three years) which was based on what he said he earned. The only reason I have involved CSA now is that in August DP and I bought a house together and exH said that he would reduce the amount of child support as a result.
Well what a result...the monthly payment will be £295 more than he has been paying for the DC until now!