Bashar al-Assad was branded the "rat of Damascus" after fleeing to Moscow as his brutal regime collapsed.
Foreign Secretary David Lammy slammed Assad as a “monster” as the horrors of his prisons, where thousands of political inmates were locked up, tortured, and killed, were emerging.
"There were those who used to call Assad the lion of Damascus,” he told MPs in the Commons.
“Now we see the reality: Assad is the rat of Damascus, fleeing to Moscow with his tail between his legs."
The Cabinet minister stressed that the new Government had chosen not to reengage with Syria under Assad's rule.
He told MPs on Monday: "We said no because Assad was a dictator, whose sole interest was his wealth and his power. And we said no because Assad is a criminal who defied all laws and norms to use chemical weapons against the Syrian people.”
He said the fall of the Assad regime was also a “humiliation” for Russia and Iran.
He said: “We welcome the opportunity this brings the people of Syria.
“Assad’s demise is not just a humiliation to him and his henchmen, it is a humiliation for Russia and Iran. Iran’s so-called axis of resistance is crumbling before our eyes.”
Mr Lammy said Russian President Vladimir Putin has attempted to “prop up Assad for more than a decade”, adding: “All that he’s got for this is a fallen dictator, filing for asylum in Moscow.”
Meanwhile, military experts said Putin has suffered a “strategic political defeat” in Syria with transport aircraft at an air base which could be used to evacuate Russian forces.
The Russian president launched a military intervention in 2015 to prop up Assad’s regime during the Syrian civil war.
He stepped in after then US president Barack Obama decided against decisive action against Assad for breaking a “red line” in his military’s use of chemical weapons on rebel-held areas of the country.
Putin’s move was seen as showing the strength of a dictator against apparent weakness by the democratic West.
In summer 2013, MPs in the UK had rejected possible British military action against Assad’s government to deter the use of chemical weapons, after dozens of Tories joined forces with Labour to oppose the move with the shadow of the Iraq War still looming large.
Then Prime Minister David Cameron said he would respect the defeat of a government motion by 285-272, ruling out joining US-led strikes.
But with Putin’s focus and military now firmly deployed in Ukraine, the Russian president only offered limited support to Assad to keep him in power, with air strikes, as Islamist rebels swept across the country forcing him to flee into exile in Moscow.
“The rapid collapse of the Assad regime in Syria, a regime that the Kremlin helped prop up since 2015, is a strategic political defeat for Moscow and has thrown the Kremlin into a crisis as it seeks to retain its strategic military basing in Syria,” said the Institute for The Study of War.
The Washington-based think tank added: “The Kremlin reportedly secured an agreement on Dec. 8 with unspecified Syrian opposition leaders to ensure the security of Russian military bases in Syria, but the contours of this arrangement and its longevity remain unclear given the volatile and rapidly evolving political situation in Syria.
“ISW has collected strong indicators that Russia has been setting conditions to evacuate its military assets from Syria and that Russian military basing is not secure.”
It highlighted satellite imagery showing four military transport aircraft, three Il-76 and one An-124, at the Russian Khmeimim Air Base in Syria’s Latakia province “possibly in order to evacuate limited amounts of Russian military assets from the country”.
But it stressed that a far bigger operation would be needed for a full evacuation from the air base and the maritime base at Port of Tartus.
The Kremlin said on Monday that it was too early to say what the future would hold for Russia’s military bases in Syria, adding that it would be the subject of discussion with the new rulers in Damascus.
After a lightning advance of a militia alliance spearheaded by Hayat al-Tahrir al-Sham (HTS), a former al-Qaeda affiliate, Assad fled to Russia, raising questions about the two strategically-important Russian military facilities in Syria.
Asked about the future of the bases, Kremlin spokesman Dmitry Peskov said: “It’s premature to talk about it yet.”
“This is all a subject for discussion with those who will be in power in Syria,” he stressed, adding that there was “extreme instability” in the country.
Mr Lammy faced questions in the Commons over whether or not HTS will be removed from the UK’s list of proscribed organisations.
HTS is banned in the UK because of its past association with al Qaida, although its leader cut ties with the terrorist organisation and has sought to present his group as a more moderate and inclusive organisation.
Mr Lammy said: “Thus far, HTS has offered reassurances to minorities in Aleppo, Hama and Damascus. They have also committed to co-operating with the international community over monitoring chemical weapons.
“We will judge HTS by their actions, monitoring closely how they and other parties to this conflict treat all civilians in areas they control.”
When pressed further, Mr Lammy also said: “We don’t comment on issues of proscription for good reason.
“We should recognise that al Qaida killed hundreds of British citizens in barbaric attacks spanning decades and that was the original reason that this organisation, HTS, was proscribed.”
