The gap between mainstream opinion in the US about homosexuality and the views held by most evangelicals is increasing, according to new findings from LifeWay Research.

In a survey of 2,000 Americans' views on gay marriage, more than half of respondents said that homosexual behaviour was not sinful. People with gay or lesbian friends were twice as likely to say gay marriage should be legal as those who had none.

Executive director of LifeWay Research Ed Stetzer said that friendship had a lot to do with attitudes: "Those who have gay or lesbian friends are the most open to gay marriage."

Regardless of friends, Stetzer said, evangelical Christians are more likely to consider homosexual behaviour sinful.

Less than a third (30 per cent) of evangelicals say gay marriage should be legal, compared to 38 per cent among evangelicals with gay or lesbian friends. Two-thirds of evangelicals also say sex between two people of the same gender remains sinful, whether it is legal or not. This figure remains broadly similar for those with gay or lesbian friends.

More than half of non-evangelicals (54 per cent) say sex between people of the same gender is not sinful, with eight per cent unsure.

However, there is a much wider acceptance of homosexual behaviour among the population in general. LifeWay ran similar surveys in 2011, 2012 and 2014 asking whether it was sinful, and the results show a considerable decline in the number of people thinking that it was. In 2011, 43 per cent said it was not a sin, in 2012 45 per cent and last year 54 per cent.

Stetzer said: "Church leaders have traditionally been seen as the champions of all things moral in society. As public perceptions of morality change, pastors find themselves in an increasingly unpopular position."