Parliament made clear two years ago that sexual infidelity should not be allowed as a defence for murder, whatever the circumstances. A partner's affair could no longer be treated by courts as a defensible reason to lose control and kill.

However, giving judgment last week, on three domestic killing appeals, Lord Chief Justice Judge ruled: "Where sexual infidelity is integral to and forms an essential part of the context the prohibition does not operate to exclude it."

It seems that parliament says infidelity doesn't count and the court says it does.

Killing a wife for infidelity was "classic" provocation under the law prior to 2009. The courts were littered with cases in which men blamed their partner's adultery for making them kill her.

In the case of Morgan James Smith in 1999, Lord Hoffman noted that historically one of the legal justifications for killing due to losing self-control had been finding a wife in adultery. It was regarded as "the highest invasion of property".

In 2008 Justice for Women asked a senior judge why he had accepted a plea of guilty to manslaughter instead of murder, when a man had stabbed his wife in fury.

"Because it was classic provocation," he said. "She was leaving him for another man. I would have been practically ordering them [the jury] to give a verdict of manslaughter!"'

Lord Hoffman, again in the case of Smith, understanding that this still prevailed, said: "Male possessiveness and jealousy should not today be an acceptable reason for the loss of self-control leading to homicide."

And that is what this legislation attempted to do. The exclusion of infidelity as an allowable trigger for a loss of self-control defence was not because legislators thought it didn't make both men and women angry but because it is contrary to modern public policy to allow it as a defence to murder.

Lord Judge accepted that the statute does not allow infidelity to be a "qualifying trigger" capable, in law, of causing someone to lose self-control but, because all the circumstances at the time of the killing have to be examined. If infidelity is present it has to be looked at and may add to the potency of any other conduct which might cause a loss of self-control. So if there can no longer be an infidelity defence there is instead a sort of "infidelity plus" defence, notwithstanding the statute says: "In deciding whether a loss of self-control had a qualifying trigger, the fact that a thing done or said constituted sexual infidelity is to be disregarded."

Clearly nobody in future will assert that they lost control because of infidelity. The defence will always be "infidelity plus". For example, she was unfaithful plus she goaded me about it.

Lord Judge studiedly gender-neutralised his reasoning but that does not alter the context that it has been men who kill their unfaithful partners and it is still very rare that the opposite is the case.

Consequently this is mainly a reversal for women, as well as a setback for parliament which intended to pass a law that recognised, like Lord Hoffman, that harmful culture must change. It should be appealed to the supreme court (though without Lord Phillips, who has already criticised the provision).

The campaigning women who fought for this change for women, and are devastated at how quickly the courts have undermined it, should be reassured that the new law has raised the bar considerably for those who kill and plead loss of control.

The defence is only allowed if the conduct provoking the cause of the loss of control was "extremely grave", gave the defendant "a justifiable sense of being seriously wronged" and would have made someone with "a normal degree of tolerance and self-restraint" lose control and kill as well. These are all far higher tests than before .

Further and importantly, women and men who kill their violent partners now have an equivalent plea if fear of serious violence made them lose self-control. The earlier law of provocation did not work for women, its basis being that the defendant was angered to kill and such women were not angry but afraid. At that time, the court of appeal was helpful, stretching the law of provocation to help, but it took this statute finally to end the appalling injustice which otherwise prevailed where angry men and women who killed their partners were acquitted of murder and frightened men and women who killed their abusers were convicted of it. This surely is new, good, clear-sighted justice and it is unaffected by last week's judgment on the three domestic killing appeals.

Only one of these appeals succeeded, where the trial judge followed the statute and prohibited the defence of loss of control through infidelity from going to the jury. That man, Jon-Jacques Clinton must now be retried on the defence of "infidelity plus". In the other two, while the old law might have produced acquittals both were convicted by juries rejecting their case under the narrower new law. Ironically, perhaps the same would have happened to Clinton if his defence were put to a jury. We shall soon see.

Despite the totemic setback for campaigning women, in this judgment, progress has been made in the Coroners and Justice Act and the days when one can legitimately say, as many protesters did about this case last week "Justice for who? Not for women" ought, in this aspect of the law of murder, at least, to be moving towards a close.

• Follow Comment is free on Twitter @commentisfree