Concern is growing that the Child Support Agency, established in April, is penalising men who are already paying agreed maintenance, instead of targeting fathers who have paid nothing.
Citizens Advice Bureaux are being inundated with complaints about the agency's assessment that an absent parent must pay far higher levels of maintenance. In one case, a father from Bideford, Devon, was forced to increase payments from pounds 9 to pounds 90 a week.
In some cases, higher levels are being enforced even though the divorced couple have agreed an amicable settlement in which the ex-wife takes the home, or equity on it, and the father pays low maintenance in exchange. The new assessment takes no account of many expenses the absent parent may incur.
When the Child Support Act was set up, ministers said its main purpose was to force absent parents - 10 per cent of whom are mothers - who paid no child maintenance to make a contribution. They said it was wrong that the taxpayer should be supporting single parents.
But leaked documents last month revealed that agency staff were being told to target middle-class parents to review payments to help meet the Government's target of saving the Treasury pounds 530m this year. Parents who already have court orders are easiest to trace.
Over the next three years, every parent on income support or family credit, who is separated from his or her partner, must have the maintenance payment reassessed by the Child Support Agency. Many people on income support have court orders and in most cases maintenance is being increased substantially.
Income support is then withdrawn and if the mother's income rises above the level of income support, she also loses welfare payments such as housing benefit, council tax benefit and free prescriptions. As a result, in some cases fathers are paying more, but the mother and children are worse off.
Over the next three years mothers who are not on income support and who have no court order can also apply for an assessment from the agency. However, from 1997 any ex-wife who is not on income support and who has a court order can apply to the agency to uprate the payment. In such cases the mother and children could be much better off.
According to Janet Allbeson, social policy officer of the National Association of Citizens Advice Bureaux, branches have had hundreds of requests for help and information from fathers, new wives and ex-wives, who say they are losing out.
New partners, such as Julie Moore (see separate story), are aggrieved because their income is taken into account when the agency decides whether the father is able to afford the assessment payment.
Ms Allbeson said: 'Absent fathers are aghast at how much they are having to pay, even when there has been a clean break and amicable settlement and in some cases the ex-wife has remarried. They feel very resentful and aggrieved. They feel they have been responsible, have paid a fair amount, and have not been feckless.
'The formula is very, very harsh and ruthless. In one case a father from Yorkshire, whose ex-wife and children moved to the south of England, was left with pounds 40 a week after the agency's maintenance assessment. After paying for other outgoings, he could no longer afford to travel to visit his children or pay for them to visit him.'
On Friday, the Independent reported the case of Les McLean, a father from Co Durham, who was ordered to pay pounds 480 a month instead of the pounds 120 a month set by a court order. Later this month he is mounting the first legal challenge to the new system by seeking to overturn the judge's decision to revoke the court order.