New laws which give householders the right to deploy "disproportionate force" against intruders in their homes are under attack at the High Court for being "incompatible" with the European human rights convention.
The so-called "householder defence" was introduced by a former Justice Secretary, Chris Grayling, who said his intention was to "toughen up" the laws on self defence "for those who defend themselves and their loved ones".
The new regime is being challenged by the family of Denby Collins, 40, a man who allegedly entered a house in Gillingham, Kent, as an intruder and was then seriously injured and left in a coma.
Paul Bowen QC, acting for the Collins family, asked two judges in London to overturn a decision of the Director of Public Prosecutions (DPP) not to prosecute the homeowner, who for legal reasons can only be referred to as "B", for causing grievous bodily harm, either with or without intent, contrary to the Offences Against the Person Act 1861.
The DPP concluded in September 2014 that any prosecution must fail because of the high hurdle presented by the householder defence, which was introduced in April 2013 - just months before Mr Collins suffered his injuries in the early hours of December 15 2013.
Asking the judges to intervene, Mr Bowen submitted to the president of the Queen's Bench Division, Sir Brian Leveson, and Mr Justice Cranston that the toughened laws were incompatible with Article 2 of the European Convention on Human Rights (ECHR), which safeguards the right to life.
Mr Bowen said the householder defence had resulted in insufficient legal protection for Mr Collins, who had suffered a life-threatening assault.
The defence was inserted into the Criminal Justice and Immigration Act 2008 after Mr Grayling promised disproportionate force would be allowed so that the public would be left in no doubt that "the law is on their side".
Mr Grayling stated in November 2012, as the changes to the law proceeded through Parliament: "Householders who act instinctively and honestly in self defence are victims of crime and should be treated that way. We need to dispel doubts in this area once and for all."
Force which is "grossly disproportionate" remains illegal.
Before the changes, section 76 of the Criminal Justice and Immigration Act 2008 said the degree of force used in self-defence must be "reasonable in the circumstances" as the person acting genuinely believed them to be.
The current Justice Secretary, Michael Gove, is defending the Government's decision to amend the law.
Clare Montgomery QC, appearing for the Justice Secretary, submitted that householder defence was not incompatible with Article 2 as it only applied to "a limited class of private individuals in residential premises".
It also only permitted a disproportionate degree of force to be used on an intruder if it was "reasonable in all the circumstances".
Mr Bowen told the court the claim that Denby Collins was an intruder who entered B's house uninvited was not accepted by Mr Collins' family, but today's case was being heard on the basis that B had an "honest if mistaken opinion" that he was "an intruder".
The QC said if the Collins family won its case the DPP would be asked to take a fresh decision whether or not to prosecute B, and for that reason B's identity was continuing to be protected.
The judges reserved judgment and said they did not expect to give their decision before Christmas.