The government is facing a new court battle to keep arms shipments flowing to Saudi Arabia, after campaigners filed a judicial review against the policy.
The Court of Appeal imposed a block on new arms sales to the autocracy in June 2019, but the government lifted it following a review in July 2020.
Now Campaign Against the Arms Trade, which responsible for the original court action, is seeking a judicial review of the decision by ministers to overturn the ban.
International trade secretary Liz Truss was branded "deeply cynical" by human rights groups like Amnesty International for arguing that apparent war crimes by Saudi forces in Yemen had been isolated incidents.
She said there had been no pattern to apparent violations of international humanitarian law and that the ban imposed by the court was therefore not justified.
But the government could now be forced by the courts to again halt the sign-off of new licences.
"Tens of thousands of people have been killed in this brutal bombardment, yet arms companies have profited every step of the way," said Andrew Smith of Campaign Against Arms Trade.
"These arms sales have only fuelled the destruction and prolonged the conflict. Last year the Court of Appeal found that the government has acted illegally, and nothing that we have seen since suggests otherwise.
"The government may think that the widespread destruction of schools, hospitals and homes can be dismissed as 'isolated incidents' but we do not. These arms sales are immoral, and we are confident that the Court will confirm that the decision to renew them was illegal.“
The controversy particularly focuses on the war in Yemen, where the oil-rich kingdom is intervening against Houthi rebels on behalf of its allies in the country's internationally-recognised government.
The UN's aid arm has described the situation as a humanitarian catastrophe, but since the bombardment began in March 2015 the UK has licensed £5.4 billion worth of arms to the Saudi regime.
Records show these arms licences, approved by ministers, include £2.5 billion worth of so-called "ML4" licenses covering bombs and missiles, and £2.7 billion of ML10 licences, covering aircraft and drones.
Rosa Curling of legal firm Leigh Day said: "Our client has provided evidence to the court which shows every independent international body which has investigated specific violations of IHL by the Kingdom of Saudi Arabia (KSA) in Yemen has concluded that KSA has perpetrated repeated violations of fundamental rules of IHL.
"Such reports have been issued year after year, without any significant evidence of a change in approach or improvement in the conduct of KSA, or the avoidance or past conduct, such as the targeting of crowded markets.
"Despite this, our government has determined it appropriate to continue to arm the KSA coalition, a decision which our client considers unlawful and a decision we hope the court will overturn as a matter of priority.”
The Independent has contacted the international trade department, which oversees arms export licensing, for comment on this story.