All sales of UK weapons to Saudi Arabia should be suspended until an independent inquiry into alleged breaches of international law in Yemen has been completed, two select committees have agreed in a joint report.

The committees accuse the Saudi government of obstructing efforts to investigate the alleged violations, which human rights organisations say are the result of its campaign of airstrikes in the country.

The UK government has failed to undertake its own credible investigations, and some ministers had told parliament of checks that had not in fact taken place, the committees said.

They feared British support, principally through arms sales, was “having the effect of conferring legitimacy” on Saudi Arabia’s actions, the report said.

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However, plans to have their recommendation to suspend arms sales endorsed by the joint committee on arms controls exports (CAEC) have been blocked by opposition led by Crispin Blunt, the Conservative chairman of the foreign affairs select committee.

In a highly unusual move, the foreign affairs committee simultaneously produced its own report suggesting the legitimacy of UK arms sales should be left for a court to decide.

Even the foreign affairs committee report, however, calls for an independent UN-led investigation into allegations that Saudi Arabia has violated international humanitarian law in Yemen.

Saudi Arabia intervened in March 2015 to support the Yemeni government against Houthi rebels, who are backed by Iran and control the capital, Sana’a. The UN has put the death toll in the 18-month war at more than 10,000 people, 3,799 of them civilians. Human rights groups accuse the Saudi air campaign of routinely hitting civilian targets.

Britain has sold more than £3.7bn of arms to Saudi Arabia since the airstrikes began.

Blunt and his allies on the CAEC created a furore at a lengthy private meeting last week when they prevented the committee reaching a consensus by walking out and ensuring there were not enough MPs to form a quorum. A draft report had called for the suspension of arms sales to Saudi Arabia.

The CAEC is unusual at Westminster in that it consists of members of four different select committees – defence, business, international development and foreign affairs. Its task is to monitor the government’s licensing of arms exports. A minimum representation is required from each constituent committee for the overall joint committee to be quorate.

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Blunt’s manouevre has created ill feeling among those who believe he walked out knowing this was the only way to prevent being defeated in a vote. For his part, Blunt said he could not see how the UK could secure its strategic objectives except in an alliance with Riyadh.

The episode underlines the fragility of political support at Westminster for the UK’s continuing close relations with the country.

The joint report by the business and international development committees states: “The UK government has not responded to allegations of IHL [international humanitarian law] breaches by the Saudi-led coalition in any meaningful way and we are concerned that our support for the coalition, principally through arms sales, is having the effect of conferring legitimacy on its actions.”

Challenging the veracity of the Saudis’ defence, they also state: “We are not convinced that Saudi Arabia is best placed to investigate reports of IHL breaches and their lack of progress in reporting findings only confirms our concerns that they are obstructing the process.”

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The committees also take the government to task for asserting that it was in a position to judge whether the Saudi bombing campaign was in breach of international law and then withdrawing the claim in a series of written parliamentary answers. “These corrections not only damage confidence in cross-Whitehall coordination and competence but, more importantly, undermine the government’s view that there is no clear risk that UK arms licensed to Saudi Arabia will be used in violations of IHL in Yemen.”

They single out Philip Dunne, the then minister for defence procurement, saying he gave a series of assurances about UK checks on the Saudi bombing campaign that the government has since admitted did not take place.

The Conservative MP Chris White, who chaired the inquiry into the exports and is a member of the business committee, said: “ The government can no longer wait and see and must now take urgent action, halting the sale of arms to the Saudi-led coalition until we can be sure that there is no risk of violation.”

In the Lords, however, the foreign office whip Annabel Goldie insisted Britain operated one of the most robust arms export control regimes in the world.

“The key test for our continued arms export to Saudi Arabia is whether there is a clear risk that those weapons might be used in the commission of a serious violation of law.

“Having regard to all the information available to us we assess that this test has not been met.”