Saudi Arabia has "privately accepted" that one of its coalition warplanes bombed a funeral in Yemen on Saturday, according to the BBC's security correspondent, Frank Gardner. Gardner's report appears to be based on a briefing from British government officials.

At least 140 mourners died in the bombing and more than 500 were injured. Video evidence shows it was a "double tap" attack – where a second strike is launched as rescuers move in to help victims of the first strike.

'Unquestionably' a war crime

Last month Britain's foreign secretary, Boris Johnson, described double tap attacks as "certainly" and "unquestionably" a war crime. At the time, Johnson was referring to Russian double tap bombings in Syria. It remains to be seen whether he will take the same view of double tap bombing by Britain's Saudi friends in Yemen.

Evidence from fragments at the scene of the funeral massacre shows that at least one of the bombs was a 500-lb American-supplied Mark 82, which is sometimes fitted with a British-made guidance system. It is not yet known which country supplied the aircraft used for the attack.

So far, despite ample evidence of Saudi war crimes in Yemen, the British government has fiercely resisted calls to suspend arms sales to the kingdom but the latest atrocity may prove too horrific for the government to brush aside.

Several previous Saudi-led airstrikes have hit hospitals in Yemen as well as civilian neighbourhoods, prompting calls for an independent international investigation – which the British government has so far opposed.

Independent investigation rejected

Saudi Arabia says the funeral massacre will be investigated by the Joint Incidents Assessment Team (JIAT) which includes representatives from countries fighting alongside the Saudis in Yemen.

Given the kingdom's history of untruthfulness regarding its actions in Yemen, this on its own is unlikely to have much credibility. Following Saturday's attack the Saudi coalition spokesman, Brig Gen Ahmad Asiri, initially denied there had been any Saudi-led military action in the area at the time and hinted at possible "other causes" of the bombing.

In a bizarre radio interview last May, Asiri falsely claimed that Human Rights Watch had not been in Yemen investigating air strikes – on the grounds that "no one can get in Yemen without the permission of the coalition". 

While opposing an independent investigation, the British government seems to recognise that an investigation by the JIAT alone is unlikely to be very convincing. According to Gardner's BBC report, Britain has asked to participate in the investigation and the Saudis have agreed to that. Gardner adds:

"An official with the UK government said Britain was considering sending a team of lawyers and military investigators to monitor the Saudi-led coalition's own inquiries."

The British government seems determined to avoid suspending arms sales to Saudi Arabia if it possibly can. The test it has set itself is whether weapons sold by Britain "might be used in a commission of a serious breach of international humanitarian law". Its answer – before Saturday's attack and despite plenty of evidence to the contrary – was that the test had not been met.

However, it's difficult to see how the government can realistically hope to maintain that position now. 

There has been no suggestion so far that Saturday's attack was off-target. The results of the "double tap" also reinforce the view that the bombs struck where they were meant to strike.

There may be questions about whether the attack had been properly authorised. If it had not, this would cast doubt on the Saudi military's command system and possibly its internal discipline too. 

A much bigger question is why the funeral was targeted. The most likely explanation is that the Saudis received intelligence that some senior Houthi-connected figures would be attending and saw it as an opportunity to kill  them. 

However, the Saudis were surely aware that Arab funerals – especially those of well-known figures like Ali al-Rowaishan – attract large numbers of people. They could also have deduced, from the size of the hall where it was held, that hundreds if not thousands would be attending.

On that basis the British government really ought to suspend arms sales to Saudi Arabia now, rather than waiting for the outcome of the investigation, since there is no guarantee that similar things won't occur again in the meantime. By the British foreign secretary's own definition, what happened on Saturday was a war crime.

Bomb fragments found

Fragments from the scene of the attack indicate that at least on of the bombs was a Mark 82, manufactured by the American company, Raytheon. One of the first western journalists to visit the site – ITV News correspondent Neil Connery – found one fragment which a Yemeni ordnance officer identified as coming from a Mark 82.

Yesterday Ammar Alaqi, a Yemeni, posted a photo on Twitter which he said had been taken by a police officer who is a trusted friend. It appears to be part of the tail fin for a Mark 82 and carries the product code "96214 ASSY 837760-4". The number 96214 shows that Raytheon was the manufacturer and 837760-4 is the part number. A slightly different photo of the same object has been posted elsewhere on Twitter and there is also a short video.

Last November the US State Department approved the sale of 8,020 Mark 82 "general purpose" bombs to Saudi Arabia. 

Mark 82 fragments have been found at the scene of other bombings in Yemen, and they can be fitted with various kinds of guidance systems. One used in an attack on the Sanaa Chamber of Commerce in January was identified by Human Rights Watch as having a Paveway laser guidance system manufactured in Britain.