THERESA May is facing fresh calls to suspend arms sales to Saudi Arabia after campaigners won a landmark legal challenge against the UK Government in a “monumental” court ruling today.

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.

Giving judgement in London, the Court of Appeal ruled 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 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.

Congratulating the CAAT Jo Swinson, the Liberal Democrats’ deputy leader, said: “Saudi Arabia is an enemy of British values, including human rights and the rule of law. Their repeated violation and disregard for human rights should have ruled them out as an arms trading partner long ago.

“Instead the Conservative Government have continued to export arms and equipment to this brutal regime. The situation is inexcusable and cannot continue. This court ruling is monumental,” declared the East Dunbartonshire MP aiming to become her party’s leader.

"It is now clear for all to see; the UK arms sales to the Saudi regime are unlawful.

“The Liberal Democrats are clear that the only acceptable course of action by the Tory Government is to suspend them immediately, rather than continuing to allow arm sales to a country which is targeting innocent civilians," she added.

Stephen Gethins, the SNP’s Foreign Affairs spokesman, said: “Today’s court ruling that the UK Government’s arms sales to Saudi Arabia are unlawful is welcome and a damning indictment of the Tory government’s flawed foreign policy approach that has led to a humanitarian catastrophe in Yemen.

“The decision must now serve as a wake-up call for the UK Government and it must now urgently re-think its strategy and instead seek to become a player for peace in the country."

The Fife MP noted how earlier this year the UN launched its largest ever single country appeal, aiming to raise £3.2 billion to support NGOs working in Yemen.

But he pointed out: "The UK Government’s arms sales to Saudi Arabia eclipse the UN’s total appeal by more than a billion pounds at a staggering £4.6bn since the war began in 2015.

"The UK Government should be ashamed of its role in the war in Yemen," declared Mr Gethins.

“Germany, Canada, Spain, Finland, Denmark, the US Congress and EU Parliament have all taken a principled stance against further arms exports to the Saudi regime as a direct result of the war in Yemen.

“Rather than being on the wrong side of history, the UK Government must get its act together and support efforts to bring this war to an end," he added.