It's nice to see that David Cameron knows about the Manga Carta because i doubt if 99% of Brits know but we assume it was something very important, which it was if you were a noble but for the vast majority of the country it wasn't much use at all.
The story goes that King John of England was forced to sign The Magna Carta so he and whoever followed him onto the throne could no longer ride roughshod over their subjects.
In reality, The Magna Carta provided plenty of personal rights and freedoms if you were wealthy because it was the landowners and Barons who wrote the Magna Carta and forced King John to sign it because they were outraged that he kept putting up their rent.
Not so much motivated by a sense of great injustice at King John’s acts of cruelty and murder against his subjects, more because he was trying to squeeze more money out of them.
The Magna Carta wasn't even an original piece, it was copied from the Charter of Liberties that Henry I signed in 1100 promising to respect certain rights of the Church and the Barons.
Far from being the basis of all English law, of the original 61 clauses, only 3 remain which are the freedom of the Church of England, the continued ancient liberties of the City of London and that no freeman shall be denied Justice or Right.
There's nothing in the charter to corresponding to a right of a citizen and Oliver Cromwell dismissed it as the 'Magna Farta' and said that it 'tied one sort of people to be slaves to another; Clergy and Gentry have got their freedom, but the common people still are, and have been left servants to work for them.'
Politician's like to portray the idea that signing of the Magna Carta was when the common man gained his rights but actually, the only beneficiaries were the English nobility and the Church of England, the rest of us continued to toil in the fields under the control of the Barons who treated the common folk with much more disdain than King John ever treated the nobility.
So next time a politician quotes the Magna Carta in order to push through some unpopular law, unless it is regarding the ancient liberties of London, the freedom of the Church or the justice of a freeman, the probability is very high that he or she is bluffing because everything else has been swept to one side, deemed as not important, by those same people.