Britain is at risk of being prosecuted for war crimes because of growing evidence that missiles sold to Saudi Arabia have been used against civilian targets in Yemen’s brutal civil war, Foreign Office lawyers and diplomats have warned. Advisers to Philip Hammond, the Foreign Secretary, have stepped up legal warnings that the sale of specialist missiles to the Saudis, deployed throughout nine months of almost daily bombing raids in west Yemen against Houthi rebels, may breach international humanitarian law. Since March this year, bombing raids and a blockade of ports imposed by the Saudi-led coalition of Sunni Gulf states have crippled much of Yemen. Although the political aim is to dislodge Houthi Shia rebels and restore the exiled President, Abed-Rabbo Mansour Hadi, thousands of Yemeni civilians have been killed, with schools, hospitals and non-military infrastructure hit. Fuel and food shortages, according to the United Nations, have brought near famine to many parts of the country. Amnesty International, Human Rights Watch (HRW) and other NGOs, claim there is no doubt that weapons supplied by the UK and the United States have hit Yemeni civilian targets. One senior Foreign and Commonwealth Office (FCO) legal adviser told The Independent: “The Foreign Secretary has acknowledged that some weapons supplied by the UK have been used by the Saudis in Yemen. Are our reassurances correct – that such sales are within international arms treaty rules? The answer is, sadly, not at all clear.” Although the Department for International Development recently received assurances from the Saudi government that it did not want a famine to develop on its doorstep, there is concern within the FCO that the Saudi military’s attitude to humanitarian law is careless. Officials fear that the combination of British arms sales and technical expertise used to assist bombing raids on Yemen could result in the UK being hauled before the International Criminal Court on charges relating to direct attacks on civilians. Another government lawyer warned: “With Britain now expected to join the United States and France in the war on Isis in Syria, there will be renewed interest in the legality of the assault in Yemen. It may not be enough for the Foreign Secretary to simply restate that we have yet to carry out any detailed evaluation [of UK arms used in the bombing of Yemen].” The legal adviser said: “Yemen could be described as a forgotten conflict. Inside the Foreign Office a course-correction is seen as crucial.” Oliver Sprague, Amnesty International’s arms trade director, told The Independent: “There is a blatant rewriting of the rules inside the FCO. We are not supposed to supply weapons if there is a risk they could be used to violate humanitarian laws and the international arms trade treaty – which we championed. It is illogical for Philip Hammond to say there is no evidence of weapons supplied by the UK being misused, so we’ll keep selling them to the point where we learn they are being used.” Most of Saudi’s weapons are supplied by the United States. With help from the UK, the US is also offering logistical support, airborne refueling, with a specialist Pentagon-approved team providing intelligence on targeting. This month the Obama administration authorized a $1.29bn (£858m) Saudi request to replenish stocks of specialist missiles, a move seen by critics as an effort to assuage Saudi anger over the US-brokered nuclear deal with Iran, the kingdom’s key regional rival. In July, Britain authorized the transfer of Paveway IV missiles from the RAF to Saudi Arabia. The MoD approved a switch in positions on an order book from the arms manufacturer, Raytheon UK. The contract, worth close to £200m, secured the supply of hundreds of the air-launched missiles to the Saudi air force over the next two years. The Raytheon precision weapons are used by both the RAF and its Saudi counterparts on Typhoon and Tornado fighter jets, supplied by BAE Systems. The order switch ensured that the Saudi arsenal, depleted through multiple daily bombing raids on Yemen over the past nine months, would not be exhausted. This week both Amnesty and Human Rights Watch issued new evidence, based on their own field research, which they said showed that a factory in the Sanaa governate that was not involved in any military production, was destroyed by a UK-made cruise missile.