A new analysis of the 2011 census shows that a decade of mass immigration helped mask the scale of decline in Christian affiliation among the British-born population – while driving a dramatic increase in Islam, particularly among the young.

It suggests that only a minority of people will describe themselves as Christians within the next decade, for first time.

Meanwhile almost one in 10 under 25s in Britain is now a Muslim.

The proportion of young people who describe themselves as even nominal Christians has dropped below half for the first time.

Initial results from the 2011 census published last year showed that the total number of people in England and Wales who described themselves as Christian fell by 4.1 million – a decline of 10 per cent.

But new analysis from the Office for National Statistics shows that that figure was bolstered by 1.2 million foreign-born Christians, including Polish Catholics and evangelicals from countries such as Nigeria.

They disclosed that there were in fact 5.3 million fewer British-born people describing themselves as Christians, a decline of 15 per cent in just a decade.

At the same time the number of Muslims in England and Wales surged by 75 per cent – boosted by almost 600,000 more foreign born followers of the Islamic faith.