British weapons sales to Saudi Arabia could be ruled unlawful after the second round of legal action by campaigners was given the go-ahead.

Judges have granted the Campaign Against the Arms Trade (CAAT) permission to appeal a ruling by the High Court in July that allowed the UK to continue granting export licences despite allegations British weapons had been used to kill civilians in Yemen.

The fresh case against the Secretary of State for International Trade will be heard by the Court of Appeal in the coming months.

Lawyers representing CAAT argued that the decision to grant the licences was against British arms export policy, which states that the government must deny applications “if there is a clear risk that the items might be used in the commission of a serious violation of international humanitarian law".

Supported by charities including Amnesty International, Human Rights Watch and Oxfam, they claim that the ongoing civil war in Yemen, where the UN says Saudi-led forces have been bombing “trapped civilians” in support of president Abdrabbuh Mansur Hadi's government, is such a risk.

Giving permission for the appeal at the Court of Appeal on Friday, Lord Justice Irwin and Lord Justice Flaux said that the criterion was put in place by legislation under the Export Control Act 2002, in response to obligations arising from the United Nations Arms Trade Treaty 2013 and from a common position adopted by the European Union.

The judges warned that the law did not permit "political considerations" or opinions on the outcome of Saudi bombing to override the ban on exporting weapons that could be used to commit war crimes.

"It is obvious that withholding this licence, or renewal of this licence, is likely to have significant implications for the international relations of the United Kingdom, and potentially for employment," they added.

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"[Political considerations] might include, for example, anticipation of the consequences of the cessation of arms sales to Saudi Arabia, including a judgement as to whether that would likely make matters worse rather than better in Yemen. However, such considerations do not form part of the criteria for the grant or withholding of a licence to export arms.

"Parliament did not permit sales, otherwise in breach of the criteria, to be justified on such a basis. They are considerations extraneous to the decision and to the legality of the decision."

The government said that it operates “one of the most robust export control regimes in the world” and keeps sales under careful review to meet standards of the Consolidated EU and National Arms Export Licensing Criteria.

CAAT says that while thousands of people have been killed in Saudi-led bombing, and many more as a result of an ongoing humanitarian “catastrophe” and famine, the UK has licensed £4.6bn worth of arms sales to Saudi Arabia.

According to official figures, £2.7bn were in a category including aircraft, helicopters and drones, and another £1.9bn including bombs and missiles.

Andrew Smith, of CAAT, said: “The Saudi-led bombardment of Yemen has killed thousands of people and created one of the worst humanitarian disasters in the world.

“Despite this, the Saudi regime has been armed and supported every step of the way by successive UK governments.

“We believe that these arms sales are immoral, and are confident that the Court of Appeal will agree that they are unlawful.”

Rosa Curling, of law firm Leigh Day, said evidence shows a “clear risk the arms sold from the UK might be used in serious violation of international law”.

The situation in Yemen Show all 14 1 /14 The situation in Yemen The situation in Yemen Houthi supporters trample on a US flag during a gathering mobilizing more fighters into several Yemeni battlefronts, in Sana'a, Yemen EPA The situation in Yemen People carry the coffins of men, who were killed in the recent Saudi-led airstrikes during their funeral, in the Old City of Sanaa, Yemen AP The situation in Yemen Pro-government fighters give food to Yemeni children on the road leading to the southwestern port city of Mokha. Yemeni rebels are putting up fierce resistance in a key Red Sea port city where they are encircled by pro-government force Getty Images The situation in Yemen A Yemeni stands in front of a graffiti protesting US military operations in war-affected Yemen, in Sana'a, Yemen. According to reports, US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen A Yemeni female fighter supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, takes part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen Yemeni female fighters supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, take part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen A boy shouts slogans next to pro-Houthi fighters, who have been injured during recent fighting, during a rally held to honour those injured or maimed while fighting in Houthi ranks in Sanaa, Yemen Reuters The situation in Yemen Balls of fire and smoke rise from a Houthi-held military camp following alleged Saudi-led airstrikes, in Sana'a, Yemen EPA The situation in Yemen Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty Images The situation in Yemen A Yemeni boy looks on as Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty The situation in Yemen A Yemeni boy sits amidst the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa AFP/Getty The situation in Yemen Marine One with US President Donald Trump flies with a decoy and support helicopters to Dover Air Force Base in Dover, Delaware, for the dignified transfer of Navy Seal Chief Petty Officer William 'Ryan' Owens who was killed in Yemen Getty Images The situation in Yemen US President Donald Trump aboard the Marine One to greet the remains of a US military commando killed during a raid on the al Qaeda militant group in southern Yemen on Sunday, at Dover Air Force Base, Delaware, US Reuters

“Where our politicians have sadly failed to follows UK legislation and policy, our client hopes the Court will ensure the rule of law is upheld,” she added.

The decision to grant permission for the appeal was welcomed by humanitarian agencies and charities.

Save the Children warned the “battle isn’t over yet”, following the death or injury of at least 6,000 children in Yemen.

“The UK government has both a moral and legal obligation to ensure British-made weapons aren’t killing and maiming children in Yemen,” a spokesperson added.

Rocco Blume, head of policy at War Child UK, said the “man-made tragedy” shows no sign of coming to an end.

“The UK now, more than ever, must do everything it can to help protect the lives of children caught up in this,” he added.

“All evidence shared publicly makes it clear that the UK government has blood on its hands as long as it sells arms to Saudi Arabia.”

Shane Stevenson, Oxfam's country director in Yemen, said it was impossible for the UK to support peace negotiations when it is also an “arms dealer”.