This week’s legal decision by the appeal court that UK arms sales to Saudi Arabia are unlawful finally opens the door to accountability for Britain’s role in the war in Yemen and the humanitarian disaster it has caused.

But while Thursday was a day of celebration for campaigners, now the hard work begins of trying to get the government to respect the decision.

The government says it will not allow arms exports where there is a clear risk they might be used in serious violations of international humanitarian law. Yet for the past four years, it has provided diplomatic cover for the Saudi-led coalition’s abuses committed primarily with UK and US supplied weapons.

The government has expended significant amounts of energy in trying not to know, or be seen to know, about those abuses. At every turn, in response to every criticism the government has mobilised doubt and ambiguity about what can be known about the conduct of the war and stuck to its claim to have one of the most robust control regimes in the world.

The court of appeal concluded on Thursday that the government has failed to assess the risk of misuse properly, as it has made no assessment of whether there is a past pattern of violations by the Saudi-led coalition in Yemen. The trade secretary, Liam Fox, whose signature goes on arms export licence approvals, has already tried to minimise the significance of the decision and indicated that the government intends to appeal.

Liam Fox delivers a speech on the future of exports from the UK after Brexit. Photograph: Leon Neal/Getty Images

New data from Yemen indicates 11,700 civilian fatalities from direct targeting – two thirds of whom have been killed by the Saudi-led coalition – and famine and cholera continue to decimate the population. As the pursuit of accountability continues, three things are worth noting.

First, this decision sticks the final nail in the coffin of the tired argument that arms sales bring influence and leverage. The government has repeatedly claimed that its friendly relationship with Saudi Arabia brings special levels of insight into, and influence over, its conduct of the war. Yet the court was clear that without assessing whether there have been breaches of international law, and whether the training has actually made any difference to how the coalition is fighting the war, all this talk about training, support and influence are moot. The government uses this argument about leverage to justify what it wishes were true and to facilitate ongoing arms exports and diplomacy, rather than as an accurate description of reality.

Second, the decision vindicates the value of open-source information coming from non-governmental organisations and the UN. The government sought to diminish the significance of open-source information, claiming superior – but secret – information from intelligence and military sources. The court of appeal recognised that NGOs and the UN had representatives on the ground in Yemen who were able to bring evidence into the public domain of likely violations of international humanitarian law, and that their methods are rigorous and reliable. This is a significant victory for activists – and especially for the Yemeni and Yemen-based researchers, journalists, and fixers who undertake this work at great personal risk.

UN officials monitor the removal of sandbag barricades in the embattled Yemeni Red Sea port city of Hodeida. Photograph: AFP/Getty Images

Lastly, there has been significant effort within government to try to manage information, minimise paper trails, and not create a record of how it was (failing to) assess risk. The court drew attention to an undocumented Ministry of Defence decision in 2016 that there would be no attempt to answer the question of whether the Saudi-led coalition was breaching international law. And last week it was revealed that the Foreign Office has repeatedly sought to delay the release of information about its processes. It is now clear there has been a cross-government effort to minimise the possibility of scrutiny and accountability.

So what now? The court has found government policy to be unlawful, so the government has to make fresh decisions, this time lawfully. The government has committed not to issue new licences to the Saudi-led coalition for weapons to be used in the Yemen war. Deliveries under existing licences are not automatically suspended in the meantime – although that would be a prudent precautionary move, if the government were serious about correcting its policy. Parliament has a crucial role in keeping up pressure on the government to put this into practice. The parliamentary Committees on Arms Export Controls must resume their role as scrutineers of government policy and put Yemen firmly back on the agenda. Given that the current and former foreign secretaries are vying to be the country’s next prime minister, the task of accountability has never been more urgent.

Dr Anna Stavrianakis is a senior lecturer in international relations at the University of Sussex