In an open letter to The Times newspaper Christians including Baroness Cox, Lord Alton and Rev Giles Fraser urge Britain to stop negotiating with Sudan in its attempts to reduce migration from eastern Africa.
It's after Amnesty International claimed (video, below) Sudan had repeatedly used chemical weapons in the Jebel Marra area of Darfur since January 2016. The charity estimates 250 people may have died from their use, most of them children.
The Sudanese government has categorically denied using chemical weapons.
The suspected chemical attacks come amid a military offensive launched in January 2016 by Sudanese forces in Jebel Marra against the Sudan Liberation Army/Abdul Wahid (SLA/AW), who they accuse of ambushing military convoys and attacking civilians.
The open letter calls for an international investigation into the Sudanese government's alleged actions.
It said: "The regime has by now realised it can defy international law, by bombing schools and hospitals, using cluster munitions and even gassing civilians with impunity.
"The UK government has stepped up its dialogue with Sudan's government to secure concessions on stemming migration from the Horn of Africa. But is it worth doing business with a regime that chemically maims and murders its citizens?
"If we want Britain to remain a moral voice on the global stage, the answer must be 'no'."
The Sudanese government said: "The foreign ministry would like to express its absolute rejection of the allegations of the report of Amnesty International and regard them as baseless and fabricated accusations.
"The report aims at crippling Sudan's efforts to complete the procession of peace and stability, realize economic development and enhance consensus and social harmony."