The archbishop of Canterbury has said “there is no such thing as an alternative fact” and called on Christian social media users to engage with an attitude of “truth, kindness and welcome” online.

Speaking at Facebook’s London office to the social network’s European head, Nicola Mendelsohn, Justin Welby expressed his concern at how “savagely social media can be used”.

“Look at any article, and then look at the comments below it and very quickly you find stuff that is just poison,” he said.

In an effort to counter the problem, the Church of England announced a set of social media guidelines, a first in the organisation’s history, built around the three precepts – truth, kindness and welcome – articulated by the archbishop.

“When you’re talking on social media, put the truth out. There’s no such thing as an alternative fact: there are opinions, and there is truth.

“When you are expressing an opinion, do so with kindness. And be welcoming: don’t throw out stuff, tweet or post things, that is a shut-out. That’s not the point of social media. It is social media.”

The Church will be following the guidelines in its postings on Twitter, Facebook and elsewhere. Welby said: “We don’t want people to lie, to act with cruelty, or to use religious jargon in a way that ontologically results in some epistemological confusion – to use some religious jargon… it’s the golden rule that Jesus Christ talks about: treat others as you would like to be treated.”

A livestream was broadcast to an online audience of 300, a small group compared with the larger crowds who tuned in to watch the archbishop leading bible studies when Facebook Live was a newer platform. The select audience may have missed Welby apparently coming down on the side of reform of Britain’s upper chamber of parliament, when he said that, sitting in the House of Lords, “you just think: why am I here?”

The archbishop acknowledged the fraught nature of a role which carries political power but must steer clear of partisan politics. When asked if it is tempting to share his own personal views, he said: “Yes, of course it is. I think the rule is – everyone is political. Even asking that question is political.”

Giving an example of where some felt the church strayed into political territory, Welby said: “Although it’s marvellous that churches are involved in food banks, it would be even more wonderful if there were no food banks. That’s not a comment on any political party, and it’s not a political position to take.”