Britain cannot be allowed to become a "God-free zone" devoid of religious faith, the Archbishop of Westminster has warned.

Cardinal Cormac Murphy-O'Connor, who is nearing the end of his term in office as spiritual leader of the one million Mass-attending Roman Catholics of England and Wales, said: "Our life together in Britain cannot be a God-free zone and we must not allow Britain to become a world devoid of religious faith and its powerful contribution to the common good."

Delivering a lecture at Westminster cathedral, Cardinal Murphy-O'Connor said Christians should treat non-believers with "deep esteem" and said they might be partly responsible for the decline in religious faith in Britain.

The Cardinal, who came under attack this morning from the academic atheist Professor Richard Dawkins and secularist organisations such as the British Humanist Association, was attemping to offer a personal perspective on faith in Britain today.

He said: "In Britain today there is considerable spiritual homelessness. At the same time as there is a lot of public interest in religion. Many people have a sense of being in a sort of exile from faith-guided experience. They think that even if they wanted to believe, faith is no longer an option for them. "

He attributed this to the "privatisation of religion" where faith was seen as a matter of personal need rather than an objective truth.

Defending his own religion of Christianity, he continued: "One of the aims of the Christian religion is to create and foster a culture and society in which human beings flourish and God is glorified by his presence in a holy people."

Religion could not be removed from the public space and banished to the church premises, he said.

"There are social currents today that want to isolate religion from other forms of knowledge and experience in order to marginalise it.

"One of the things which I challenge is the desire to separate Christianity from rational inquiry. Many of our ‘new atheists’ seem unable to cope with the notion of an intelligent, reflective Christian faith. But the Catholic Christian tradition is characterised by a close relationship between reasoned understanding and religious faith. Faith for us is the flowering of reason, not its betrayal."

Referring to Professor Dawkins, he said people from his perspective rejected a God that no Christian believed in in any case. "I simply don’t recognise my faith in what is presented by these critics as Christian faith."

Dr Dawkins, author of books including The God Delusion, defended himself against the Cardinal's criticism. He told BBC Radio 4's Today programme that God was no more than an "imaginary friend".

He said: "When talking to a politician you would demand proof for what they say, but suddenly when talking to a clergyman you don't have to provide evidence. There's absolutely no reason to take seriously someone who says, 'I believe it because I believe it. God either exists or he doesn't. It's a matter of the truth."

Andrew Copson of the British Humanist Association said: "Those of us campaigning for a secular state are not out to deny the right of religious people to participate freely and equally in the public sphere. What we do want is an end to religious privilege, such as the state-funding of faith schools, bishops sitting as of right in the House of Lords, and exemptions from equality law such as those that the Cardinal lobbied for. In a society as diverse as modern Britain, religious and non-religious people alike need the sort of free public space that only secularism can provide."