Partial defence to the crime of murder in the jurisdiction of England and Wales
The loss of control defence is a partial defence to the crime of murder in the jurisdiction of England and Wales. It was created by section 54 of the Coroners and Justice Act 2009. The definition of "loss of control" in the Act is defined in a way that requires multiple requirements to be met, and with a number of listed exceptions that can render the defence inapplicable.
In particular, for a defendant to rely on the defence, there must either be "fear of serious violence", or the combination of "circumstances of an extremely grave character" and a "justifiable sense of being seriously wronged". Revenge for sexual infidelity is specifically ruled out as a qualifying trigger, although "R v Clinton" has interpreted this exception as applying only to cases where sexual infidelity is the "single" cause of loss of control.
The loss of control defence does not exonerate the person who loses control; instead it downgrades the charge for that person from murder to manslaughter, and does not change the nature of the offence for other perpetrators who may have been involved. 
The partial defence of loss of control was introduced to replace the partial defence of provocation, which was abolished by the same legislation.
References.
 ;templatestyles src="Reflist/styles.css" / ;