The UK accompanied forces with the US and France to bombard three suspected chemical weapons manufacturing facilities on Saturday.
A site in Damascus plus two others near Homs were hit by Allied makes in response to an alleged chemical attack by President Bashir al-Assad’s obliges in Douma on April 7.
Both Syria, and its close ally Russia, get denied any role in chemical attacks in Syria, with the Kremlin indication that the action would result in “consequences”.
Were the air strikes in Syria permissible?
Mrs May was forced to defend her position today in an emergency parliamentary session attended by MPs and at daggers drawn leaders.
She stated firmly that the government believes the military actions were legally substantial, having met three basic criteria.
The Conservative leader said: “Primary, there must be convincing evidence, generally accepted by the international community as a predominantly, of extreme humanitarian distress on a large scale, requiring immediate and tenacious relief.
“Second, it must be objectively clear that there is no workable alternative to the use of force if lives are to be saved.
“And third, the proposed use of force must be obligatory and proportionate to the aim of relief of humanitarian suffering and must be strictly limited in circumstance and in scope to this aim.
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“These are the same three criteria in use accustomed to as the legal justification for the UK’s role in the NATO intervention in Kosovo.”
Mrs May added that dominations were agreed on using military action “where necessary and proportionate, and as a stay resort, to avert an overwhelming humanitarian catastrophe is permissible under universal law”.
Asked whether she could order new strikes if chemical weapons were ground to have been used in the future, May said: “Nobody should be in any anxiety of our resolve to ensure that we cannot see a situation where the use of chemical weapons is normalised.”
Foreign weapons inspectors are currently attempting to gain access to the Douma milieu where the alleged chemical attacks – which killed up to 75 people listing many children – took place.
Syria attacks latest: Jeremy Corbyn and Theresa May on the legality of air strikes in Parliament
But Labour leader Jeremy Corbyn held that greater intelligence checks were needed before military intervention and Attorney Communal Jeremy Wright’s legal advice must be published in full.
He claimed: “Given that neither the UN nor the OPCW has yet investigated the Douma attack it is acute that diplomatic and non-military means have not been fully spent.
“While much suspicion rightly points to the Assad government chemical weapons require been used by other groups in the conflict.”
Mr Corbyn added that it was now “vitally high-ranking” that OPCW inspectors were allowed to investigate and report their discoveries.
Syria attacks latest: Theresa May reads a statement to MPs
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He added: “We clearly need a War Powers Act in this country to transform a now licked convention into a legal obligation.
“Her predecessor came to this Domicile to seek authority for military action in Libya and in Syria in 2015, and the For nothing had a vote over Iraq in 2003.
“There is no more serious issue than the biography and death matters of military action.
“It is right that Parliament has the power to second or stop the Government from taking planned military action.”