The sight of Government and Opposition leaders coming together to announce an agreed solution to a political problem is all too rare in this country. It is rare because a problem unresolved is normally grist for the mill of the party out of power. The "anti-smacking bill" was no exception.

Deeply unpopular, it was going to play against the Government whatever happened. Though sponsored by a Green MP, Sue Bradford, it had the support of the Labour caucus and it is Labour that would have borne the outrage if it passed or the jeers if it had failed. It was an issue the Government could not win and National could not lose.

Why, then, has National come to the rescue? Commentators will be hard-pressed to find a self-serving motive. Perhaps they will decide that leader John Key had more to gain by appearing conciliatory on this issue than the subject was likely to be worth to him at the next election. If that was his calculation, it does not reduce the credit he is due for inviting a genuine solution.

Both sides want to stop serious assaults on children; neither wants to see parents prosecuted for a smack.

The agreed solution is simple and ought to have been obvious all along. Seldom has public debate raged so long on a subject where the two sides differed so little. Both sides want to stop serious assaults on children; neither wants to see parents prosecuted for a smack. The debate has been about the wording of legislation to satisfy the agreed purpose.

One side has insisted that the bill must not state any degree of permissible violence if it is to convey the right message to those households where a hiding is considered reasonable punishment. The other side has maintained that unless the bill expressly permits a light smack, reasonable parents will be at risk of prosecution.

The solution announced yesterday between the Prime Minister and Mr Key is to put a rider in the bill stating that the police have the discretion not to prosecute a parent for the use of force against a child if "the offence is considered to be so inconsequential that there is no public interest in proceeding with a prosecution".

No degree of assault will be legislatively permitted.

The important distinction from the present Crimes Act, which allows parents to use "reasonable force", would seem to be that discretion is passed from the courts to the police. At present a parent who is prosecuted for assault can invoke the statutory defence and it is up to a court to decide whether the force was reasonable. If the bill passes with the agreed instruction to the police, they will have the discretion to prosecute and no degree of assault will be legislatively permitted.

In essence the rider formalises the view of the bill's proponents that the police will not waste their time prosecuting parents for a normal smack. It will be up to the police to decide what is "consequential" and common sense should tell them. Opponents of the bill might wonder whether psychological consequences could be argued by prosecutors to outlaw the slightest corporal punishment but it is unlikely.

The most important consideration is whether the latest alteration helps or hinders the message the bill is intended to send to parents and would-be parents who have been reared with brutal discipline, believe it normal and believe the law allows parents to administer it. That misconception has to change.

The law will no longer allow children to be beaten by anyone.

"Reasonable force" was never intended to cover some of the hidings it has excused. The stormy debate that has accompanied the attempt to expunge the parental defence to assault is in danger of sending a mixed message to abusers. Now it is important that the concluding agreement leaves no doubt that the law will no longer allow children to be beaten by anyone.