Campaigners have won a landmark legal challenge against the Government over UK arms sales to Saudi Arabia.
Campaign Against Arms Trade (CAAT) argued that the decision to continue to licence 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.
Giving judgment in London today, the Court of Appeal ruled that "the process of decision-making by the Government was wrong in law in one significant respect".
Saudi Arabia is a major customer of BAE Systems and its partners in the Eurofighter consortium.
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 Terence added: "The decision of the court today does not mean that licences to export arms to Saudi Arabia must immediately be suspended."
He said the Government "must reconsider the matter" and estimate any future risks in light of their conclusions about the past.
BAE Systems Air employs around 10,000 people at its sites at Warton and Samlesbury
It makes the Eurofighter Typhoon and the Hawk trainer jet, which are both sold around the world, and sections of the American F-35.
Andrew Smith of Campaign Against Arms Trade 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.
"The bombing has created the worst humanitarian crisis in the world. UK arms companies have profited every step of the way. The arms sales must stop immediately."
Speaking outside court, Lloyd Russell-Moyle, who sits on the House of Commons' Committee on Arms Export Controls, demanded a public inquiry into the sales of UK arms to Saudi Arabia.
He also called on the Government to "do the honourable thing and immediately suspend" arms sales.
The Labour MP for Brighton Kemptown said International Trade Secretary Liam Fox "is not the right person to continue looking at this and that is why an independent inquiry needs to be set up".
Mr Russell-Moyle said: "Boris Johnson, when he was foreign secretary, was involved in these licensing decisions, and a number of times approved the licences that we are talking about."
He added: "These failings go to the very top of the Conservative Party and the Government."
Making a statement to the House of Commons, International Trade Secretary Liam Fox said: "The Government has always taken its export control obligations very seriously and continues to do so.
"There were three grounds of appeal. The judgment found in the Government's favour in two of these grounds and against in the other.
"We disagree with the judgment against the Government on ground one and will seek permission to appeal (against) the judgment."
A BAE Systems’ spokesman said: “We note the decision by the Court of Appeal directing the UK Government to revisit one specific aspect of its decision-making process for granting export licences for the sale of military equipment to Saudi Arabia. BAE Systems is not party to the proceedings.
“We continue to support the UK Government in providing equipment, support and training under government to government agreements between the United Kingdom and the Kingdom of Saudi Arabia.
“We will assess the result of the UK Government’s reconsideration of its decision-making on the basis set out by the court, once it has been made.
“BAE Systems has a well-established legal and regulatory compliance structure for ensuring adherence to all relevant export control laws and regulations in the countries in which it operates.”