The archbishop of Canterbury has said a no-deal Brexit would hit the poorest and most vulnerable people in the UK.

Justin Welby also said he was praying for Theresa May and other politicians at the start of what is expected to be one of the most tumultuous weeks in recent parliamentary history.

Last week, Welby said in the House of Lords that a no-deal Brexit would be “not only a political and practical failure, but a moral one,” and a second referendum may be needed to avoid it.

He repeated his concerns in an interview with Christian website Premier, saying: “The burden of proof is on those that are arguing for no deal, to show that it will not harm the poorest and most vulnerable … How we care about them and how our politics affects them is a deeply moral issue.”

He added: “Politicians have one of the hardest jobs in the world. It is deeply difficult, and we need to pray for them. It is unbelievably difficult.

“When I pray for Theresa May and for all of our politicians, which I do every day … [I pray for] wisdom, courage and strength for them and their families, and for them internally, their psychology, their sense of wellbeing … We entrust them with more responsibility than any of us could cope with.”

Welby is known to have voted remain in the 2016 referendum, and has described the EU as “the greatest dream realised for human beings since the fall of the western Roman empire”.

But since the referendum he has stressed the need for reconciliation. Supporters of remain and leave must exercise restraint in their language, he has urged. People and political leaders needed to “calm down the hatreds that have arisen over the last few years, [so] that we will move towards reconciliation,” he said last month.

Previously he has indicated that he is opposed to a second referendum. But he told the House of Lords last week: “A second referendum is not my preference, but if parliament fails in the task entrusted to it, then regrettably it may be required. This is about more than Brexit, and parliament must not show itself unfit for the job.”

A recent opinion poll found that 44% of Britons thought it was inappropriate for the archbishop to offer political opinions, compared with 35% who said it was appropriate.