The Archbishop of Canterbury, the head of the Church of England, has warned Christians that their views on sexual orientation were beginning to look like an "atrocious injustice".

Justin Welby spoke at the opening of the Evangelical Alliance on Wednesday. During a question and answer session after his speech, the archbishop was asked why he voted against same-sex marriage legislation.

"What I voted against was what seemed to me to be the rewriting the nature of marriage in a way that I have to say within the Christian tradition and within scripture and within our understanding is not the right way to deal with the very important issues that were attempted to be dealt with in that bill," he replied.

"The bill was clearly, quite rightly, trying to deal with issues of homophobia in our society," Welby continued."As I said at the time in the House of Lords, [...] the church has not been good at dealing with homophobia -- it has at times, as God's people, either implicitly or explicitly supported it and we have to be really, really repentant about that because it is utterly and totally wrong."

Welby said he didn't support same-sex marriage, but he warned the Church's view was quickly becoming out of touch.

"We have to face the fact that the vast majority of people under 35 not only think that what we're saying is incomprehensible but also think that we're plain wrong and wicked and equate it to racism and other forms of gross and atrocious injustice. We have to be real about that."

Watch listen to audio, uploaded to YouTube, below: