Less than a third of people younger than 40 identified as Christian with 56% saying they had no religion at all.
The poll, conducted by YouGov last month with a sample of 1,500 across the whole population, found that 54% of people over the age of 40 in the UK identified as Christians.
Forty percent in the same age bracket said they had no religion but one in six of those agreed there was probably a higher power.
The poll has appeared in the Sunday Times but will be published on Tuesday by Linda Woodhead, professor in sociology and religion at Lancaster University.
It's reported she will blame the Church's attitude to divorced and gay people for the figures, which show a further decline in British Christianity.
"Most Anglicans and Catholics are not like their leaders. They are liberal about personal morality and more right wing politically but their leaders are more conservative in personal morality and more left wing politically," she told the paper.