The Pew Research Centre in America said Christianity currently enjoys the majority religion status in the UK with more members than any other religion or atheism put together.
But the report says by 2050 Christianity will go into the minority with just 45.4% identifying themselves as followers of Christ.
In contrast the number of atheists will have increased to 38.9%.
Christianity will still be the UK's top religion in 2050 but added together the country's other faiths will make up more of the population.
The study also found that Islam will be the largest religion in the world in 2100.
It highlighted that despite an expected increase in the number of the Christians in the world Islam will still be the dominant religion.
Researchers said: "By the year 2100, about 1 per cent more of the world's population would be Muslim (35 per cent) than Christian (34 per cent)."
Professor David Voas, an expert on religious population changes at the University of Essex, spoke on Premier's News Hour.
He said: "Christianity is going to continue to grow, particularly in the Global South, on the African continent especially. But you're right, in relative terms, it's Islam that will be the big gainer of the next few decades.
"A revival could change things considerably and if we had some remarkable great awakening it could turn things round completely, but those sorts of things are epoch-making events and are not to be taken for granted.
"I think the big uncertainty in China... The Chinese government has been anti-religion traditionally and Christianity in particular has suffered over the last century from suppression.
"Now, if that were to change... then I think it's very likely that we could see a substantial growth in the Christian population, and that would of course change the balance of the global population."