“For the next three hours I urge members to just focus on Syria,” the Labour MP Alison McGovern asked of her colleagues at the start of Monday's debate, after the UK joined in airstrikes on Syria. “They deserve that.” It was no surprise to veteran Syria watchers that the leader of her party, Jeremy Corbyn, responded to this simple request by spending a quarter of his speech talking about Yemen.

Corbyn’s frequent calls for diplomacy over the conflict in Syria sound reasonable, and certainly have the support of many voters. Yet the Labour leader often treats Russia as a good-faith actor in the conflict, even as it pumps out propaganda in support of the Assad regime. Corbyn's executive director of strategy and communications, Seumas Milne, meanwhile, has a reputation for being, in his former life as a journalist, sympathetic to Russia. More recently, he is said to have suggested that Russia's involvement had stabilised the region.

In light of this, Corbyn's quest for peace looks like something else: a willingness to repeat Russian propaganda and implicitly support its intervention in the conflict, but not intervention by the west.

In his opening speech on Monday, Corbyn referred to the inspection of the Assad regime’s weapons facility in 2017. The Organisation for the Prohibition of Chemical Weapons inspected two sites, Barzah and Jamraya, between February and March of that year (the Him Shinsar facility mentioned by Corbyn in his speech was not referred to in the 2017 OPCW report, but was a target of the most recent strikes). On 4 April 2017, chemical weapons were reportedly used against the civilian population in the the Khan Shaykhun area of southern Idlib, a rebel-held region, with children listed among the 80 dead. Three days later, the US launched an air strike on an Assad regime airbase.

Corbyn quoted a line in the July 2017 OPCW report, which stated: “the inspection team did not observe any activities inconsistent with obligations”. The same line is repeated in a Russia Today article, alongside regime denials that the facility was a chemical weapons factory.

Look closer at the OPCW report, though, and it becomes clear that the regime refused to allow OPCW inspectors on site for an entire month. It also ignores the political restraints governing weapons inspectors: in late 2017, Russia used its UN security veto to block the OPCW’s Joint Investigative Mechanism, responsible for investigating responsibility for chemical weapons attacks in Syria.

The Labour leader also used his speech to allege that chemical weapons have been used by “other groups” in the conflict, referring to an alleged chlorine attack in Aleppo in 2016 blamed on the Saudi-backed rebel group Jaish al-Islam. The single incident in question was reported by Amnesty International, although it has never been verified by the OPCW. The claim that Jaish al-Islam are responsible for using chemical weapons is murky at best, despite their many other crimes. There are only two actors in the Syrian war that have been confirmed to have used chemical weapons by the OPCW: the Assad regime and Isis.

Corbyn also dedicated part of his speech to Yemen. While the conflict in Yemen is undoubtedly appalling, and Western governments have been one-sided in their intervention, perspective is needed. At 10,000 casualties, the death toll in Yemen is 50 times lower than the more than half a million dead estimated in Syria. Nor has any side in Yemen been found guilty of using chemical weapons, which is the charge levelled against the Assad regime - and the rationale for the strikes being debated in parliament. Why talk about another conflict altogether except to avoid the issue of chemical weapons use in Syria?

Is it really possible for the man that was once known as “the Left’s foreign secretary” to get basic priorities so wrong? Corbyn has been here before. In 2013, the then backbencher was chair of the Stop The War Coalition. Shortly after the regime’s chemical weapons atrocity in Eastern Ghouta, Stop the War invited a pro-regime nun, Sister Agnes, who claimed children in footage of the attack were simply “sleeping”, to present the regime’s case (Sister Agnes withdrew after the ensuing protest).

On the face of it, his Stop the War credentials do suggest that Corbyn is consistently against intervention. Much has been said of his inability to think of a scenario in which he was willing to deploy British forces. Yet a 2015 interview published in the Observer reported that Corbyn opposed military intervention in Syria, but supported Russian troops being there, if they were there for peacekeeping purposes. (Labour sources say Corbyn’s intention was to speak in support of UN peacekeepers).

Corbyn’s 2015 view may be more nuanced than it was presented on paper, but there are reports of a similar view put more bluntly by his spokesman Seumas Milne. At a private event in London early last year, two witnesses report hearing Milne, during the course of a conversation, remark that “the situation had improved” since Moscow entered the fray and had brought “stability” to the conflict. (A Labour source said: “The claims about Seumas Milne's views and comments are nonsense.”)

Public statements from the Labour party have on occasion sought to downplay Russian involvement in international conflicts. In October 2016, as public concern about the plight of civilians in Syria mounted, a senior spokesperson for the Labour leader declared: “The focus on Russian atrocities or Syrian army atrocities I think sometimes diverts attention from other atrocities that are taking place.” Milne was named by Labour MPs as the spokesperson responsible for a statement put out by the leader’s office which questioned the evidence that the Kremlin was to blame for the poisoning of a former Russia spy in Salisbury.

On the surface, Corbyn has one constructive argument: that Britain should avoid unilateral or multilateral military action, and work through the UN. Yet this, too, is disingenuous. Russia continuously uses its security council veto to block any and all meaningful resolutions on Syria. Most recently, it vetoed the very OPCW investigation into the chemical weapons attack on Douma that Corbyn had been calling for. As the situation stands, the OPCW is restricted to merely confirming whether or not such an attack took place and what substance was used, not assigning blame. Even its limited task will be difficult enough task considering Russian forces have been at the attack site for days.

Speaking to Andrew Marr the day after the airstrikes, Corbyn said: “I can only countenance involvement in Syria if there's a UN authority behind it.” This implies that he could, in theory, back UN-led intervention. Yet a close look at his record contradicts this: even when there was a UN resolution about Libya he did not support military action. In 2011, in a Guardian piece entitled “Libya and the suspicious rush to war,” Corbyn expressed his scepticism about the real intention of UN Resolution 1973 on Libya, which authorised military intervention to establish a no-fly zone, a proposal that was supported by 75 per cent of Libyans. On 21 March 2011, he voted against a parliamentary motion welcoming the use of UK military to establish a no-fly zone in Libya.

Defenders of Corbyn argue that he opposed the intervention because of the possibility of "mission creep" – and in this he was proved right. Yet when it comes to Syria, the hard truth is that the international community has been fruitlessly pushing for a political settlement for years. Diplomacy has failed repeatedly. Since Russia's military intervention, the Assad regime has regained territory, and it has no intention of negotiating a surrender in a war it is winning. Assad has openly mocked the UN process, which he says is a “game”.

This is illustrated by the plight of Eastern Ghouta. The region was supposed to be a “de-escalation” zone – a status agreed by the Russians, the regime and groups within Eastern Ghouta. Yet the Assad regime took advantage of the ceasefire to cleanse the area of opposition. It did so with impunity, precisely because there were no international mechanisms in place to safeguard a ceasefire.

After the parliamentary debate, the verdict seemed to be that most MPs backed the Prime Minister’s actions, including many from Labour. Yet some Corbynite MPs chose to shun parliament in favour of the Stop The War demonstration outside. One, Chris Williamson, said of the Assad regime's use of chemical weapons “The motive is questionable, the evidence – where is the evidence? It just isn’t there.”

Meanwhile, in her closing remarks, Alison McGovern urged the government to listen to Syrians: “The world will be a safer place if we can rebuild the simple principle that no ruler has the right to brutally slaughter their own citizens, not in Syria and not anywhere.”