Verdict due on Monday over humanitarian challenge claiming weapons may have been used to kill civilians in Yemen

Britain will be forced to suspend the sale of what potentially could be billions of pounds worth of weapons to Saudi Arabia if it loses a high-profile legal case on Monday.

The high court is due to give its verdict in a judicial review that puts arms sales export policy in the dock and has the potential to embarrass the government.

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The ruling comes at a crucial time for bilateral relations. The government has been accused of burying a report into the funding of terrorism in the UK that is believed to be particularly critical of Saudi Arabia, the largest buyer of British arms. The UK has licensed more than £3bn of arms to Saudi Arabia in the last two years alone.

Since 2015, the kingdom has waged a bombing campaign in Yemen, where thousands of civilians have died in a civil war. Saudi Arabia has backed the ousted government against Houthi rebels supported by Iran.

Since the conflict began, Britain has issued export licences for the sale of a quantities of hardware including aircraft, drones, grenades and missiles.

But Campaign Against the Arms Trade has questioned whether the licences are compatible with UK and EU legislation, given widespread concerns about the kingdom’s actions in Yemen. International organisations including a UN panel of experts, the European parliament and humanitarian NGOs have condemned the continuing airstrikes against Yemen as unlawful.

They contend that the strikes are in breach of international humanitarian law because they are being carried out with insufficient regard to the protection of civilians and civilian buildings. In some cases, it is alleged that Saudi forces deliberately targeted civilians.

The EU council common position on arms sales compels the UK to deny an export licence if there is “a clear risk” equipment might be used in violation of international humanitarian law.

In February, when the judicial review was launched, Rosa Curling from the law firm Leigh Day, which is representing Campaign Against the Arms Trade, said: “We believe that the decision taken by the secretary of state to continue to grant new licences for the sale of arms to the kingdom of Saudi Arabia is unlawful. There is increasingly evidence being unearthed that the Saudi-led coalition has committed serious breaches of international humanitarian law in Yemen.”

A ruling against the government – which would force it to suspend exports of weapons intended for use in Yemen – could have wider implications for Britain’s arms industry. It is likely to lead to further scrutiny of the sale of British-made weapons to other countries suspected of breaching international humanitarian law.

Since May 2015 Britain has licensed £140m worth of arms to Qatar, which stands accused of funding terrorists. Licences issued include those for the export of aircraft, small arms ammunition, sniper rifles and components for helicopters.

Turkey, which has imprisoned tens of thousands of people since last year’s failed coup, is another priority market for arms exporters. Britain has issued licences for the sale of more than £300m of arms to Turkey since 2015.