Your ex is liable to pay the amount stipulated in a
child maintenance agreement until it is varied (if the
consent order is less than a year old) or the order
ceases to have any effect. Until such time any arrears can be enforced like
any other debt.
However, with consent orders made after 2003
either party can apply to the CSA for assessment one year after the order
was made, the CSA notify the courts and the consent order with regard to CM
ceases to have any effect. The exceptions to this are when one parent lives
abroad, there are step-children or over 18 year olds in education.
Check out how much your ex would pay under the CSA on the calculator on
the CM Options website and if it is less than he is offering to pay it
would be worth trying to negotiate an amount somewhere between the two
figures.
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England and Wales 
Scotland 
