Labour has released legal advice which it said showed the British military strikes on Syria were illegal.
The legal opinion published on Monday, prepared by Oxford professor Dapo Akande, said the joint British, US and French action against the Syrian regime was “not in accordance with the United Nations Charter and international law”.
The government has published a section of its own legal advice which it said concluded the strikes were legal on the basis of “humanitarian intervention”.
Theresa May will today tell MPs military intervention in Syria was “Britain’s national interest”.
May has faced criticism from opposition parties and some of her own MPs for not asking for parliamentary approval before launching the attack on key chemical and military facilities in Syria.
Jeremy Corbyn has opposed the action and questioned its legal basis.
Akande, a professor of public international law, said the government’s position was “significantly flawed”.
“It is quite clear that the position advocated by the government is not an accurate reflection of international law as it currently stands,” he said.
“International law does not permit individual states to use force on the territory of other states in order to pursue humanitarian ends determined by those states.”
The legal opinion was commissioned by Labour’s deputy leader, Tom Watson.
The government’s legal advice was that the UK could launch military action to “alleviate overwhelming humanitarian suffering” in order that the following three tests were met.
(i) there is convincing evidence, generally accepted by the international community as a whole, of extreme humanitarian distress on a large scale, requiring immediate and urgent relief;
(ii) it must be objectively clear that there is no practicable alternative to the use of force if lives are to be saved; and
(iii) the proposed use of force must be necessary and proportionate to the aim of relief of humanitarian suffering and must be strictly limited in time and in scope to this aim (i.e. the minimum necessary to achieve that end and for no other purpose).
May has argued the three tests were met. But Labour has said even though it rejects the legitimacy of the tests, they were not met.