People who kill their partners after years of abuse would be able to use a new defence that they had acted in response to extreme "words and conduct", under government plans to change the law on murder.

The proposals from the Ministry of Justice, to be unveiled today, would also provide a defence for women in domestic violence cases who kill their partners in premeditated attacks. They would be able to rely on a defence of "fear of serious violence" but would not have to show they acted spontaneously.

The reforms, triggered by concerns about the different treatment of men and women in cases of domestic violence, would mean the abolition of the 17th century defence of provocation and a more precise medical definition of diminished responsibility. At the centre of the reforms is tackling gender inequality: the view that it is too easy for men to say they killed female partners because of infidelity, or the ending of a relationship, while women with abusive partners find it hard to mount a similar partial defence.

"The days of sexual jealousy as a defence are over," said Vera Baird QC, the solicitor general. "Exceptionally, someone who loses control and kills from a justifiable sense of being seriously wronged by the victim's conduct will ... have a partial defence. "However, unlike the current defence of provocation, this can't be used when ordinary domestic conflicts cause friction and emphatically will not be available as a reaction to sexual infidelity."

Men and women who suffered a "slow burn" of domestic violence over a period of time could also use one of the partial defences under the proposals, overturning the law which requires them to have acted on the spur of the moment. But Maria Eagle, the justice minister, said the slow burn defence would still have a high threshold. "This is a substantial change," she said. "But we would not want to introduce anything that would allow cold, calculating killers to get away with it."

The recognition of the devastating effects of long-term domestic abuse was demonstrated by the case of Kiranjit Ahluwalia whose conviction for killing her husband was overturned on appeal in 1992. After abuse including having a hot iron held to her face, she attacked him in his sleep by pouring petrol on his feet and setting them alight, but he died and she was charged with murder.

Her appeal set a historic precedent - that women who kill as a result of severe domestic violence should not be treated as cold-blooded murderers. As in the case of Sara Thornton, Ahluwalia's story showed they could still have a defence, even if they did not kill in response to an immediate act of violence.

The proposals - which have taken more than four years to draw up after two reports from the Law Commission - do not take forward the idea of a US-style scale of first and second degree murder which was recommended in the commission's second report in 2006.

The new concept of the "words and conduct" defence could apply, for example, when a rape victim killed his or her attacker after being taunted about what happened. The partial defence could also be used when a mother kills a man after catching him trying to rape her daughter, said a Ministry of Justice spokeswoman. It could also similarly apply when neighbours have been involved in a long-running dispute, leading to one of them killing the other, although the spokeswoman said this would be a "very exceptional" case.

If a jury accepts a partial defence in a murder trial the defendant can be convicted of manslaughter instead, and receive a much lower sentence.

The defence of being in "fear of serious violence" would mean that men or women living with domestic violence could argue they were forced to kill their tormentor.

But the Ministry of Justice said the law would be changed to make it clear that someone who discovered their partner was having an affair would not be entitled to argue they had been "seriously wronged".

Lady Scotland, the attorney general said: "Murder law has not changed since 1957 - the proposed thorough overhaul will bring it right up to date."

The new partial defences in full are:

· Killing in response to a fear of serious violence.

· Killing in response to words and conduct which caused the defendant to have a justifiable sense of being seriously wronged.

Other reforms in the consultation paper include a change to the partial defence of diminished responsibility. It will be abolished and replaced with a defence based on "recognised medical conditions" with defences "grounded in a valid medical diagnosis" that together "encompass the recognised physical, psychiatric and psychological conditions".

The document says: "Where a woman has suffered mental health problems as a result of domestic abuse, this definition will enable them to be taken into account." But the government dropped a previous Law Commission recommendation for a defence of "developmental immaturity", which would have seen children who kill being convicted of lower charges lawyers proved they were young for their age.