Once again it is worthwhile looking back at the context in which the 2nd Amendment was written. Like much of the founding documents of the United States, it is what we would now call a "cut and paste" from an earlier document.
The 2nd Amendment has its roots in the 1689 Bill of Rights in England. Like the Constitution it followed a revolution - in its case the Glorious Revolution which saw the overthrow of the Catholic James II in favor of his daughter Mary and her husband William, Prince of Orange, both Protestants as co-regnants. It ended 130 years of alternating Protestant and Catholic rule. After the death of Henry VIII his daughter, Mary I, called "Bloody Mary" had tried to re-establish the Catholic church. 50 years before the suspected Catholic sympathies of Charles I had led to civil war and his execution. Like the Declaration of Independence (which again reflects its language) the Bill of Rights lays out the grievances against James II and sought to redress them.
The main charge against James II was that he
did endeavour to subvert and extirpate the protestant religion, and the laws and liberties of this kingdom.
by, among others
By raising and keeping a standing army within this kingdom in time of peace, without consent of parliament, and quartering soldiers contrary to law.
By causing several good subjects, being protestants, to be disarmed, at the same time when papists were both armed and employed, contrary to law.
Thus in setting William and Mary on the throne Parliament asserted that
taking into their most serious consideration the best means for attaining the ends aforesaid; do in the first place (as their ancestors in like cases have usually done) for the vindicating and asserting their ancient rights and liberties, declare:
....
That the raising or keeping a standing army within the kingdom in time of peace, unless it be with consent of parliament, is against law.
That the subjects which are protestants, may have arms for their defence suitable to their conditions, and as allowed by law.
A hundred years later (and in different circumstances) these two provisions were, in effect, conflated into:
A well regulated militia being necessary to the security of a free State, the right of the People to keep and bear arms shall not be infringed.
The following two hundred years saw the divergence of the two systems. On the one hand Britain relied on the supremacy of Parliament to protect the citizens' rights whereas America looked to an almost immutable document. In the course of that, the British Parliament has been free to respond to the sorts of killings we saw in Washington DC yesterday with what are among the strictest gun control measures in the world.
Two multiple murders with guns were the catalysts for these laws. In August 1987 Robert Ryan used two semi-automatic rifles and a handgun to kill 16, including his mother, wound 15 others and then shoot himself in what became known as the Hungerford Massacre. The Firearms (Amendment) Act 1988 banned semi-automatic rifles and shotguns with a capacity of more than 4 cartridges. In March 1996 Thomas Hamilton entered Dunblane Primary School with two 9mm Browning HP pistols and two Smith & Wesson M19 .357 Magnum revolvers. He killed 16 children, a teacher and finally himself. After public pressure and an enquiry, Parliament passed the Firearms (Amendment) Act 1997 and the Firearms (Amendment) (No. 2) Act 1997 which together effectively banned the possession of firearms apart from hunting rifles and shotguns used for vermin control. A few handgun permits were given out for personal protection purposes to those at a proven risk (Northern Ireland politicians for example) however even these were suspended during last year's Olympics. Special arrangements had to be put in place for the shooting events at the games - the British team are forced to travel abroad to practice these.
Of course this prohibition has not stopped gun murders in the UK. For a start the availability of shotguns and rifles leaves a loophole used by Derrick Bird in 2010 in Cumbria to kill 12, injure 11 (including blinding a policeman who eventually committed suicide) and then kill himself when cornered. Nor has it stopped criminals from using handguns. What it has done is reduce the rate of gun murders to 0.07 per 100,000 of the population England and Wales (Scotland and Northern Ireland have separate figures to reflect their different legislation but are about the same rate). By contrast the rate in the USA is 2.97 - over 42 times. (See Guardian table) The number is consistently under 50 for the whole country.