Dukey is spot on. A statement of arrangements is just a statement outlining the arrangements for children on divorce so the court can ensure adequate arrangements are in place. The statement isn''t the same thing as a Consent Order settling the finances and it isn''t legally binding and can''t be enforced.
As the finances on divorce haven''t been resolved you may agree for child maintenance be paid voluntarily but then it isn''t enforceable. You could make a binding private agreement which *may* be enforced through the small claim court.
Alternatively you can agree child maintenance and it can be included in a Consent Order as part of the divorce settlement and then any arrears can be enforced. One year after the date of the order either party can apply to the CSA.
The other option is to apply to the CSA for assessment and if necessary collection of child maintenance.