The bombing has been "barbaric" and war crimes have "unquestionably" been committed. One especially repugnant kind of bombing is known, euphemistically, as the double tap: "They drop one bomb and then they wait for the aid workers to come out, civilian people pulling the injured from the rubble, and then five minutes later they drop another bomb."

These are the bold words of Britain's foreign secretary, Boris Johnson, referring to attacks by Russia and the Assad regime in Syria – and few would disagree with them.

It was a different story at the weekend, though, when two airstrikes – yes, another "double tap" bombing – hit a funeral gathering in Yemen, killing at least 140 people and injuring hundreds more.

The normally outspoken Mr Johnson was silent and it was left to a junior Foreign Office minister, Tobias Ellwood, to issue a statement. He said he would be raising British "concerns" with the Saudi ambassador and urged the Saudi-led coalition which is bombing Yemen to investigate itself as quickly as possible.

It's very likely that British-made warplanes were involved in the funeral massacre, since Britain has been selling them to the Saudis for years. The British government also has a singular blind spot when it comes to war crimes in Yemen. The test regarding arms sales, it says, is whether weapons sold by Britain "might be used in a commission of a serious breach of international humanitarian law". Despite ample evidence that this is the case, it continues to insist that the test "has not been met".

None of this, of course, has escaped the notice of the Russians. It allows them to dismiss western protests about atrocities in Syria as an example of political game-playing. At the UN last month, Johnson's denunciation of Russia's actions in Syria was promptly slapped down by Russian foreign ministry spokeswoman Maria Zakharova who retorted that Britain should look to its own record before criticising Russia.

On that, the Russians do have a point. Britain's double standards regarding Syria and Yemen are not only making matters worse in Yemen but also undermining western policy towards Syria.

Britain's sycophantic attitude towards Saudi Arabia can also be contrasted with that of the United States. Hours before Britain had got around to saying anything about the funeral massacre, the US warned that its "security cooperation" with the Saudis was "not a blank cheque" and announced that it had "initiated an immediate review of our already significantly reduced support to the Saudi-led coalition".

"Since March 2015," Reuters reports, "Washington has authorised more than $22.2 billion in weapons sales to Riyadh, much of it yet to be delivered. That includes a $1.29 billion sale of precision munitions announced in November 2015 and specifically meant to replenish stocks used in Yemen."

Behind the scenes, though – as the Reuters article indicates – the Obama administration has been struggling to balance what it sees as a need to stay on friendly terms with Saudi Arabia against the risk of becoming a "co-belligerent" in the Yemen war under international law. As a "co-belligerent" the US would be obliged to investigate allegations of war crimes in Yemen and US military personnel might be exposed to prosecution.

Another awkward legal issue for the US – and relevant to its position on Yemen – was a ruling from the war crimes trial of former Liberian president Charles Taylor in 2013 that "significantly widened the international legal definition of aiding and abetting such crimes", according to Reuters:

"The ruling found that "practical assistance, encouragement or moral support" is sufficient to determine liability for war crimes. Prosecutors do not have to prove a defendant participated in a specific crime, the UN-backed court found."

It would be difficult for the US to ignore that ruling because it has already made use of it at a military commission hearing in Guantanamo Bay, to bolster its case that Khalid Sheikh Mohammed and other al Qaeda detainees were complicit in the 9/11 attacks.

Many Yemenis believe – not without reason – that the bombs dropped on the funeral last Saturday were American made. This probably explains why two missiles were fired (harmlessly) from Houthi-controlled territory in Yemen towards the USS Mason in the Red Sea on Sunday. 

One of the first western journalists to visit the scene of the funeral attack in Sanaa – ITV News correspondent Neil Connery – found what appeared to be a bomb fragment. A Yemeni ordnance officer told the film crew it came from an American-made Mark 82 bomb.

Just before the massacre in Yemen, Saudi Arabia announced that it would pay for the evacuation and medical treatment of 150 Syrian children injured during the fighting in Aleppo. Meanwhile, no one injured in the Yemeni funeral attack can be flown out for treatment because the Saudis are ensuring that Sanaa airport remains closed.