Family law solicitors were angered when Social Security secretary Alistair Darling illustrated the benefits of his latest white paper reforms of the child support system by using the example of 'fathers who run around in the company porsche, but plead poverty to their children'.

According to Nigel Mears, a partner in the Birmingham office of Amery-Parkes, the reality is more mundane.

'If a father has to pay too much maintenance, he won't be able to afford to take his children to McDonald's at weekends,' he explains.

Before the CSA was introduced in 1991, Mr Mears says, fathers would often reach an agreement through their solicitor involving a low level of maintenance, but with a tacit agreement that the father would, for example, buy his son's football boots.

It may not be enforceable, but in most cases the system worked because it was based on real behaviour.

'The father likes to know where his money is going,' Mr Mears adds.

If a father believes the settlement is inherently unfair, the relationship with his children suffers, he says.

'Some women have received higher payments as a result of the CSA.

But whether the children are always happier is another question.' Rosemary Carter, a partner in five-partner London firm Barnett Sampson, and chairman of the 4,000-strong Solicitors Family Law Association (SFLA), says the government is using myths to try to win the arguments.

'It might go down well with the focus groups, but it won't work in practice,' she insists.

The CSA has a history of failing to match the spin Westminster gives it.

Now the government is overhauling the rules again to make them simpler.

The absent parent -- usually the father -- will pay 15% of net income for one child, 20% for two and a maximum 25% for three or more.

Non-payers face being criminalised and may even lose their driving licences.

Solicitors accept that all systems are flawed.

In any flagrant abuse can be identified, but it is the overall effect which is important.

Never mind the theory, look at the actual deal the mothers and children are getting, they say.

The effect of the CSA, family law solicitors argue, has been to reduce the chance of a workable, negotiated settlement.

In higher-income cases the CSA can be removed from the equation by a negotiated settlement, agreed through a court, on property and maintenance for the partner and children.

Mr Mears says a deal made voluntarily is much more likely to be adhered to.

But for lower-income clients in particular, the spectre of the CSA haunts the negotiations.

And under the white paper proposals, which are determined to exclude lawyers and courts, it will no longer be possible to negotiate a deal which avoids the rigid statutory guidelines.

James Pirrie, a partner in the Family Law Consortium in London says: 'When money is tight, you have to expend more energy crafting a settlement which makes sense to the family'.

He cites a typical case under current law, where a lower-income father gives up his share of the house to provide for the mother's financial security.

'He then has to stretch himself to the limit to fund his own mortgage,' says Mr Pirrie.

'He doesn't have much spare income.' To make a settlement that is workable, Mr Pirrie adds, the father and mother muddle through on slightly lower levels of maintenance.

At the same time, the mother may attempt to retrain so that she can earn money independently.

A high CSA maintenance order throws the whole arrangement into disarray.

There is little scope for solicitors to defend clients who are being pursued by the CSA, because the procedures are fearfully complex.

There is also little hope of negotiation with the agency.

The fathers who are trying to avoid paying maintenance do not seek legal advice.

They are more likely to use an accountant than a lawyer if they are wealthy, or to have no representation at all if they are poor.

Peter Watson-Lee, a partner in Williams Thompson, a five-partner matrimonial specialist in Christchurch, Dorset, says: 'Solicitors who advise the clients on CSA have almost always come through matrimonial proceedings with them first.

The CSA is the latest wave in their negotiations'.

Mr Watson-Lee has seen the way that intervention by the CSA has often removed negotiation, compromise -- and solicitors -- from the picture.

When fathers come to him asking for help because they have received an unfair CSA demand, he says: 'All I can do is advise them on how to fill in the form asking for a re-assessment'.

The CSA's role threatens amicable relationships between former partners, solicitors insist.

Mr Watson-Lee says: 'An astonishingly high proportion of women don't co-operate with the CSA because they know the effect it will have on the husband's attitude'.

Adrian Pellman, a niche matrimonial and business practitioner in Eynsham, near Oxford, has given initial advice to fathers many times, but only once represented a client at a tribunal, which was unsuccessful.

It was three hours travelling time each way (from Oxford to Essex), and an hour and a half for the tribunal.

H e has concluded that unless there is a prospect of overturning the liability altogether, it is not viable to represent a client by personal attendance at a tribunal appealing against an assessment.

Mr Pirrie, who has represented the SFLA in negotiations with ministers, says the government is aiming for a lawyer-free system, but it will end up with an advice-free system.

The ideal, he maintains, would be straightforward rules, with an appeal to a court.

'The government says courts give inconsistent settlements,' he says.

'But you won't ever have consistency if you are taking individual circumstances into account.'