A poll has found that the majority of Americans believe equal marriage will inevitably become legal – whether they support it or not.

According to Southern Baptist Church-affiliated LifeWay Research 64% of Americans, almost two thirds, believe that same-sex marriage will be legalised.

The poll also found that significant proportions of Americans believed that certain professions should be allowed to refuse their services to same-sex couples. There is currently no national law in America preventing discrimination on the basis of sexuality, although 21 states have their own laws prohibiting it.

63% of Americans said clergy should be able to opt out of services for same-sex couples, and 58% believed photographers should be allowed to do the same.

Smaller proportions believed that housing and employment discrimination on the basis of sexual orientation should be allowed: 40% thought rental companies should be allowed to refuse gay couples, falling to 20% for landlords and 14% for employers.

President of LifeWay Ed Stetzer said: “We’re kind of in a national conversation about not just the issue of marriage and homosexuality, but really how our culture responds both to shifting views on the issue and views that aren’t shifting.

“While a majority of Americans categorize homosexuality as a civil rights issue like age, race and gender, and almost two-thirds think legalization of same-sex marriage in the US is inevitable, the research does show lines and divisions on these issues clearly exist in our country.”

He added: “Clearly, Americans believe the prerogative exists for individuals such as clergy or photographers to deny services for same-sex marriage. However, the level of agreement changes with scenarios that could be interpreted as more basic rights such as housing and employment.”

A survey released by LifeWay in January showed that 37% of Americans thought homosexuality was a sin – a drop of 7% since 2011.

A recent poll suggested Catholics are among the most progressive religious groups in America, with 54% supporting the legalisation of equal marriage.