David Cameron has used the 800th anniversary of Magna Carta to press the case for an overhaul of UK human rights laws.
The historic document had been used around the world in the promotion of human rights but in Britain these principles had "sometimes become distorted and devalued", the Prime Minister argued.
It fell to the current generation to "restore the reputation" of those rights and "safeguard the legacy" of Magna Carta.
Mr Cameron joined the Queen, senior members of the Royal Family and the Archbishop of Canterbury at Runnymede , where King John sealed the charter that limited the power of the Crown on 15 June, 1215.
The Tory Government has controversial plans to scrap the Human Rights Act and affirm the supremacy of the UK's Supreme Court over the European Court of Justice in Strasbourg.
It has left open the option of withdrawing from the European Convention of Human Rights if these reforms are blocked.
In a speech, Mr Cameron said Magna Carta takes on "further relevance today".
He argued: "For centuries, it has been quoted to help promote human rights and alleviate suffering all around the world.
"But here in Britain - ironically, the place where those ideas were first set out - the good name of 'human rights' has sometimes become distorted and devalued.
"It falls to us in this generation to restore the reputation of those rights - and their critical underpinning of our legal system.
"It is our duty to safeguard the legacy, the idea, the momentous achievement of those barons.
"And there couldn't be a better time to reaffirm that commitment than on an anniversary like this."
"So on this historic day, let's pledge to keep those principles alight."
Magna Carta inspired those who fought in the English Civil War, the Chartists, the Suffragettes, the founders of the first American states, Gandhi, Nelson Mandela and "anyone challenging injustice or checking arbitrary power", Mr Cameron said.
And it was a document everyone in Britain should be proud of.
He added: "Its remaining copies may be faded, but its principles shine as brightly as ever in every courtroom and every classroom from palace to Parliament to parish church.
"Liberty, justice, democracy, the rule of law - we hold these things dear and we should hold them even dearer for the fact that they took shape right here, on the banks of the Thames.
"So on this historic day, let's pledge to keep those principles alight. Let's keep Magna Carta alive.
"Because as those barons showed, all those years ago, what we do today will shape the world for many, many years to come."