David Cameron has said the UK is a Christian country "and we should not be afraid to say so".
In a speech in Oxford on the 400th anniversary of the King James Bible, the prime minister called for a revival of traditional Christian values to counter Britain's "moral collapse".
He said "live and let live" had too often become "do what you please".
The PM said it was wrong to suggest that standing up for Christianity was "somehow doing down other faiths".
Describing himself as a "committed" but only "vaguely practising" Christian, the PM admitted he was "full of doubts" about big theological issues.
'Don't do God'
But he staunchly defended the role of religion in politics and said the Bible in particular was crucial to British values.
"We are a Christian country and we should not be afraid to say so," he told the audience at Christ Church.
"Let me be clear: I am not in any way saying that to have another faith - or no faith - is somehow wrong.
"I know and fully respect that many people in this country do not have a religion.
"And I am also incredibly proud that Britain is home to many different faith communities, who do so much to make our country stronger.
"But what I am saying is that the Bible has helped to give Britain a set of values and morals which make Britain what it is today."
Mr Cameron said people often argued that "politicians shouldn't 'do God'" - a reference to a comment famously made by former No 10 spin doctor Alistair Campbell when Tony Blair was asked about his religion.
"If by that they mean we shouldn't try to claim a direct line to God for one particular political party, they could not be more right," the PM said.
"But we shouldn't let our caution about that stand in the way of recognising both what our faith communities bring to our country, and also just how incredibly important faith is to so many people in Britain."
Mr Cameron also said it was "easier for people to believe and practise other faiths when Britain has confidence in its Christian identity".
"Many people tell me it is much easier to be Jewish or Muslim here in Britain than it is in a secular country like France," he said.
"Why? Because the tolerance that Christianity demands of our society provides greater space for other religious faiths too.
"And because many of the values of a Christian country are shared by people of all faiths and indeed by people of no faith at all."