The Archbishop of Canterbury has conceded that Britain is "certainly not" a Christian country in terms of the number of regular churchgoers, but its society and values had been "shaped and founded on" the religion.
The Most Rev Justin Welby welcomed the debate about the position of Christianity in British society triggered by Prime Minister David Cameron's decision to speak out about his religious views, claiming that the faith was more vulnerable to "comfortable indifference" than opposition.
The archbishop said: "It is a historical fact (perhaps unwelcome to some, but true) that our main systems of ethics, the way we do law and justice, the values of our society, how we decide what is fair, the protection of the poor, and most of the way we look at society... all have been shaped by and founded on Christianity."
He added: "It is clear that, in the general sense of being founded in Christian faith, this is a Christian country.
"It is certainly not in terms of regular churchgoing, although altogether, across different denominations, some millions attend church services each week.
"Others of different backgrounds have also positively shaped our common heritage.
"But the language of what we are, what we care for and how we act is earthed in Christianity, and would remain so for many years even if the number of believers dropped out of sight (which they won't, in my opinion)."
The Prime Minister was criticised for saying "we should be more confident about our status as a Christian country" and "more evangelical" about faith in a Church Times article.
Mr Cameron also warned that people who "advocate some sort of secular neutrality fail to grasp the consequences of that neutrality, or the role that faith can play in helping people to have a moral code".
The article provoked a response from more than 50 leading public figures, organised by the British Humanist Association, warning Mr Cameron risked sowing "alienation and division" in society.
But writing on his blog, the archbishop said the response to Mr Cameron's article and supportive comments by other Cabinet ministers was "baffling and at the same time quite encouraging".
He wrote: "Judging by the reaction, anyone would think that the people concerned had at the same time suggested the return of the Inquisition (complete with comfy chairs for Monty Python fans), compulsory church going and universal tithes.
"More than 50 leading atheists wrote to the Telegraph in protest.
"It's all quite baffling and at the same time quite encouraging.
"Christian faith is much more vulnerable to comfortable indifference than to hatred and opposition."
Deputy Prime Minister Nick Clegg also gave his support to Mr Cameron, but called for the separation of church and state in England.
The atheist Deputy Prime Minister said Britain's history and heritage was "infused by Christianity" but people of "all faiths and none" were able to share values of "fair play and tolerance".
On his LBC Radio phone-in show Mr Clegg said: "I'm not a man of faith but I don't find it particularly controversial to say, if you look at our history, heritage, our architecture, our values, of course it is infused by Christianity.
"I'm slightly nonplussed by people getting very worked up about it.
"I'm not a practising man of faith but I don't find it an issue to say we have an important Christian identity in terms of our history and heritage and so on.
"That is not to say that somehow we are exclusively Christian, where everybody is a Christian or indeed that we have got one Christian denomination - there are almost as many Catholics as Anglicans in this country.
"Of course we should remember that one of the greatest Christian values - if you want to put it that way - of tolerance, is that we are open to people of other denominations, other faiths, of all faiths and none.
"It's the senses of fair play and tolerance that makes our country very special."
Mr Clegg added: "Recognising our history and our heritage and who we are and have been over several centuries doesn't mean that you have to say you are a Christian to believe in tolerance and diversity, I'm just saying that actually they are not incompatible with each other, that's all."
He said disestablishing the Church of England, separating it from the state, would be "better for Anglicans" but accepted such a change would not happen overnight.
Mr Clegg said: "In the long run, having the state and the church bound up with each other, as we do in this country, I think it would be better for the church and better for people of faith and better for Anglicans if the church and the state were, over time, to stand on their own two separate feet."