The Child Maintenance and Enforcement Commission is responsible for the child maintenance system.
I have asked the Child Maintenance Commissioner to write to the hon. Member with the information requested in respect of the current position and I have seen the response.
I should also add that as part of the development of regulations for the future child maintenance scheme, the policy affecting cases such as these is being reviewed.
Letter from Stephen Geraghty:
In reply to your recent Parliamentary Question about the Child Support Agency, the Secretary of State promised a substantive reply from the Child Maintenance Commissioner as the Child Support Agency is now the responsibility of the Child Maintenance and Enforcement Commission.
You asked the Secretary of State for Work and Pensions, if she will investigate the anomaly whereby a non-resident parent in receipt of certain benefits including pensions paid on medical grounds can receive an income of almost £25,000 per annum and the resident parent receives the minimum weekly maintenance payment of £5 per week, irrespective of the number of children involved. 
Non-resident parents in receipt of prescribed benefits will only be assessed as being able to pay the £5 per week flat rate of maintenance. This is not affected by the amount of benefit paid.
It is possible for the parent with care to apply for a variation on the grounds that the non-resident parent receives other income which has not been taken into account. The Child Support (Variations) Regulations 2000 specifically provides for the initial £5 per week maintenance liability to be varied where the non-resident parent receives other income, which would have otherwise been taken in to account in the initial maintenance calculation process, were it not for the fact that the non-resident parent was receiving a prescribed benefit.
I hope you find this answer helpful.