Since 2004, mothers and fathers have risked prosecution if they injure children with a slap
Lenient punishments should be given to parents who "accidentally" injure their chldren smacking them, judges have said.
Since 2004, mothers and fathers have risked prosecution if they injure children with a slap.
But sentencing rules set down by the Lord Chief Justice and his colleagues appear to make Labour's law unworkable.
The judges said parents who are prosecuted for accidentally injuring their children with a smack should not be jailed or given serious penalties.
In many cases, those brought to court should be discharged with no punishment, said the Sentencing Guidelines Council, which lays down rules that judges and magistrates must follow.
The 2004 law says anyone who causes injury to their children with a smack is guilty of actual bodily harm. A bruise, reddened skin or psychological injuries, can bring a jail sentence of five years.
But the judges say courts should give great weight to the defence of "reasonable chastisement", which has allowed parents to smack since the 1860s. Labour's Children Act removed that defence from parents who cause injury.
However, Lord Phillips, the most senior judge in England, and his colleagues, said courts should take it as "substantial mitigation".
If a parent had not meant to injure and had not foreseen any injury, they would have intended nothing illegal, the paper said.
"Such a finding of fact should result in a substantial reduction in sentence and should not result in a custodial sentence.
"Where not only was the injury neither intended nor foreseen, but was not even reasonably foreseeable, then a discharge might be appropriate."
The Council set down its views in a draft set of guidelines on how to sentence those guilty of assault or cruelty against children. The rules are likely to be sent to the courts next year.
It follows the launch of a Government consultation that could lead to laws outlawing smacking.
Tim Loughton, Tory spokesman on children, said: "The smacking law has brought utter confusion and is completely unworkable."
The Council, which is dominated by judges, also said sentences for assaults on adults and for attempted murder should be more lenient.