The High Court will rule later on whether the government has unlawfully failed to suspend the sale of UK fighter jets and bombs to Saudi Arabia.
More than £3.3 billion worth of arms has been sold to the Gulf state since it began bombing neighbouring Yemen in March 2015.
The Campaign Against Arms Trade (CAAT), which has brought the case against the government, said at least 10,000 people have been killed as a Saudi Arabia-led coalition intervenes in the Yemeni civil war.
The CAAT claims the coalition is guilty of “repeated and serious breaches” of international humanitarian law, and created a humanitarian catastrophe – destroying vital infrastructure and leaving 80% of the population in need of aid.
However the government insists there is no “clear risk” that UK licensed items might be used to commit a serious violation of humanitarian law.
Government lawyers say in a written statement before the court that it is relying on “all of the information available” – some of which “may not be publicly available”.
But Martin Chamberlain QC, appearing for CAAT, said the evidence to be presented in open court was enough on its own to show that “no reasonable decision maker” could have allowed the sale of arms to Saudi Arabia to continue.
Mr Chamberlain said the evidence included a large number of authoritative reports and findings from bodies including Amnesty International, Human Rights Watch, Oxfam and Rights Watch (UK) who were making submissions to the court.
CAAT was also relying on reports from an expert panel appointed under a UN Security Council resolution, other UN bodies and officials and from the EU Parliament.
The QC said the findings of those bodies “establish an overwhelming case that the Kingdom of Saudi Arabia-led (KSA) coalition has committed repeated and serious breaches of international humanitarian law in Yemen”.