Tony and Trayvon Martin. Not related by blood, but the two share more than a surname. The supporters of both men claim that they are the victims of unfair self-defence laws in their respective countries. Whereas in the UK, Tony Martin was deemed to have unlawfully killed the burglar who had entered his farmhouse, Trayvon Martin’s killer has walked free from a Florida Court. In seeking to avoid the issues caused by Tony Martin’s prison sentence, the UK government has made worrying moves towards the much-criticised US position.

The “stand your ground” self-defence law in Florida, states that a person who is attacked in a place where he or she has a right to be has “no duty to retreat and has the right to… meet force with force, including deadly force if he or she reasonably believes it is necessary to do so”.

In the aftermath of the Zimmerman trial, the United States Attorney General, Eric Holder called into question “laws that senselessly expand the concept of self-defence and sow dangerous conflict in our neighbourhoods”. The veteran campaigner Reverend Al Sharpton went as far as to describe the stand your ground law, which exists in over 30 States as the “worst violation of civil rights” in America. If the dry words of the legal text books do not provide enough context, perhaps the fact that this law is supported strongly by the National Rifle Association will.

Opponents argue that by allowing a lawful excuse for people to stand and fight when faced with what they perceive to be a grave threat, the law will lead to unnecessary escalations in violence. When this is coupled with ingrained racial stereotyping which perceives certain races to be more threatening than others, the law can justify or even catalyse a deadly chain of events.

Ironically, it is a variant of the stand your ground law – in fact a more extreme form – that the coalition has just written into the statute books.

In 2012, Justice Secretary Chris Grayling grandly declared: “The public should be in no doubt that in such circumstances that the law really is on their side. We need to get rid of doubts in this area once and for all”. Contrary to Grayling’s version of events, the law prior to his amendment was appropriate to deal with the situation of people threatened in their own homes: a person was allowed to use such force as is reasonable, in the circumstances which he honestly believed to be the case. This rule took into account the possibility for an honest mistake about the level of threat that an intruder poses but crucially, did not act as a carte-blanche for acts of personal revenge or retribution. Sometimes, it is reasonable to not use force at all.

The law did not impose an onerous duty on the initial victims of a crime to carefully consider absurd trade-offs: “Should I hit him with a vase, or use a golf club?” The statute books, judges, and perhaps most crucially, the Crown Prosecution Service did not expect a person to, as one Law Lord put it “weigh to a nicety” the exact measure of a defensive action. Fortunately, this remains unchanged in all situations apart from that of the household.

One recent amendment provides that a possibility that a defendant could have retreated is to be as a factor to be taken into account in deciding whether force was reasonable, rather than as giving rise to a duty to retreat– in other words, this is a statutory endorsement of the stand your ground law. More importantly though, s.43 of the Crime and Courts Act 2013, which came into force this April, provides that in a household case (the definition of which is complex), the degree of force used by a defendant is “not to be regarded as having been reasonable” in the circumstances as the defendant believed them to be “if it was grossly disproportionate in those circumstances”. This ungainly negative formulation will only serve to confuse matters. It appears that some level of disproportionate force will be available to householders, but precisely what degree is entirely unclear. How does one distinguish what is merely disproportionate from grossly disproportionate?

Chris Grayling’s bluster is liable to cause two problems. First, the new law will create more rather than less confusion, second it may even encourage people to think that acts of vigilantism are now ratified. As the Trayvon Martin case has demonstrated, this can go horribly wrong. In their knee-jerk reaction to the cases like that of Tony Martin, the government risks opening the door to the tragedy of his namesake.