Yesterday the United States, Britain and the UN's special envoy issued a joint call for a rapid and unconditional ceasefire in Yemen.

"We are not calling for this in a vacuum," US secretary of state John Kerry said; there have been "communications" with representatives of the Houthis who control much of Yemen and with Abd Rabbou Mansour Hadi who is still regarded internationally as the country's president.

"I have talked with the foreign minister of Oman," Kerry said, "as well as with the foreign minister of Saudi Arabia and of the United Arab Emirates, and everybody agrees that the moment calls for moving forward with efforts to try to de-escalate and find a way forward at the negotiating table."

Significantly, the ceasefire call follows a major embarrassment for the anti-Houthi side. On Saturday, the Saudis admitted that their bombing of a funeral in Yemen which killed at least 140 people and injured hundreds more on October 8 was a tragic blunder. The attack, an official report said, had not been properly authorised and was based on false intelligence provided by one of Hadi's Yemeni affiliates. The kingdom is now offering tocompensate the families of victims and has set up a $53 million fund "to facilitate the transfer abroad of the injured who need to be treated".

This debacle is forcing the US and Britain – the main sources of weapons for the Saudi-led bombing campaign – to reconsider their position. Metal fragments from the scene of the funeral massacre indicate that at least one of the bombs used was American-supplied and possibly fitted with a British-made guidance system.

The US reacted sharply to the funeral attack, announcing "an immediate review of our already significantly reduced support to the Saudi-led coalition". 

Since the start of the bombing campaign in March last year the US has never been particularly enthusiastic about it and has sometimes cast doubt on the Saudis' military competence. American support for intervention in Yemen was mainly intended to placate the Saudis over the Obama administration's nuclear deal with Iran.

The British government – always fearful of offending the Saudis for commercial reasons – has been less openly critical but has nevertheless got itself into a muddle over arms supplies. 

The legal test is whether these supplies "might be used in a commission of a serious breach of international humanitarian law". Until last July, despite growing evidence of attacks of civilians in markets, hospitals and elsewhere in Yemen, the government repeatedly said "we have assessed that there has not been a breach". In July, it quietly "corrected" all previous statements by admitting that no such assessment had been made – which further increased political pressure for a halt to arms sales.

An added complication is that the funeral attack was a "double tap" where a second strike occurred as rescuers moved in after that first bomb hit. Speaking last month in the context of Russian "double tap" bombings in Syria, Britain's new foreign secretary, Boris Johnson, said such attacks were "unquestionably" a war crime.

Given the Saudis' admission of serious flaws in their command system, it is now even more difficult for the British government to claim there is no risk of its weapons being used in contravention of international humanitarian law.

This background provides some context to yesterday's ceasefire call and also shows that the US and Britain have quite a lot of leverage in terms of implementing it. They could – if they chose – bring the bombing campaign to a halt by cutting arms supplies or perhaps by just threatening to do so.

Over the last year and a half the Saudi-led military intervention has cost billions of dollars as well as thousands of lives and the situation in Yemen is now worse than it was before:

• A food crisis is affecting more than half the population, according to the UN, and 1.3 million children are acutely malnourished. 
• The coalition has failed to dislodge the Houthis from the capital, Sanaa, and they still control large swaths of the country.
• Hadi – the "legitimate" president, as the Saudis call him – looks even less legitimate and presidential than he did before.
• Yemen is now, in effect, partitioned – north and south – and unless that changes the Saudis can expect to have the Houthis as a long-term neighbour.
• The war has created a space for al-Qaeda and IS to flourish.
• The war has exacerbated sectarian divisions.

These are all good reasons for demanding a ceasefire in the hope of moving forward towards some kind of political settlement. However, it's unlikely that a ceasefire can be established without serious loss of face by the Saudis and, to a lesser extent, other members of the coalition.

In its early stages, the intervention in Yemen was often characterised as part of a more "muscular" and "assertive" Saudi foreign policy – a policy which now appears to have failed its first big test. This may also cause some collateral damage to Prince Mohammed bin Salman, the king's favourite son, who is Saudi Arabia's defence minister (among many other things) and was the main driving force behind the intervention.

Even if the Saudis accept a ceasefire it's still unclear whether the Houthis will. The UN envoy seems to have had positive indications but the Houthis can be unpredictable and might see some advantage in forcing the Saudis to carry on fighting.

A year ago the Washington Post suggested Yemen was "turning into Saudi Arabia’s Vietnam" but in some ways it's worse than that. When the US pulled out of Vietnam it was at least clear who would take over. The same can't be said of Yemen which, for most purposes, is now a failed state and likely to remain so for a long time.

Even if a ceasefire does take effect in the next few days progress will be needed on the political front in order to make it last. We can hope, but the prospects for a sustainable political solution still look extremely slim.