Campaigners have won a landmark legal challenge against the government over its decision to continue to allow UK arms sales to Saudi Arabia.
Campaign Against Arms Trade (CAAT) argued that the decision to continue to license military equipment for export to the Gulf state, which is leading a coalition of forces in the Yemeni conflict, was unlawful.
The group said export licences should not have been granted as there was a clear risk that the arms might be used in a serious violation of international humanitarian law.
Judges at the Court of Appeal in central London ruled on Thursday that "the process of decision-making by the government was wrong in law in one significant respect".
Announcing the court's decision, Master of the Rolls Sir Terence Etherton, sitting with Lord Justice Irwin and Lord Justice Singh, said the government "made no concluded assessments of whether the Saudi-led coalition had committed violations of international humanitarian law in the past, during the Yemen conflict, and made no attempt to do so".
Sir Terrance said the ruling "does not mean that licences to export arms to Saudi Arabia must immediately be suspended".
The government "must reconsider the matter" and estimate any future risks in light of their conclusions about the past, he added.
CAAT called on International Trade Secretary Liam Fox to reconsider the export licences in accordance with the correct legal approach.
Andrew Smith, from CAAT, said: "We welcome this verdict, but it should never have taken a court case brought by campaigners to force the government to follow its own rules.
"The Saudi Arabian regime is one of the most brutal and repressive in the world, yet, for decades, it has been the largest buyer of UK-made arms.
"No matter what atrocities it has inflicted, the Saudi regime has been able to count on the uncritical political and military support of the UK."
A Downing Street spokeswoman said the government was "disappointed" with the judgment and was looking at an appeal.
A government spokesperson said: "This judgement is not about whether the decisions themselves were right or wrong, but whether the process in reaching those decisions was correct.
"We disagree with the judgment and will be seeking permission to appeal."
Labour MP Lloyd Russell-Moyle, who sits on the House of Commons' Committee on Arms Export Controls, demanded an independent public inquiry into UK arms sales to Saudi Arabia.
Speaking outside the court, he said ministers should "do the honourable thing and immediately suspend" arms sales.