Polls in recent days have shown public wariness of military intervention in Syria, with Britain still haunted by its participation in the US-led invasion of Iraq. The dangers of bombing now, which could escalate the conflict beyond belief.
Labour leader Jeremy Corbyn said the military action against Syria was "legally questionable" and makes real accountability for war crimes less likely.
Senior government ministers were summoned back from a spring break to discuss the attack last week in Douma, which has sparked a tense confrontation between Western nations and Syria and its allies, led by Russian Federation.
"We don't want bombardment which leads to escalation and a hot war between the USA and Russian Federation over the skies of Syria", he added. He added: "Theresa May should have sought parliamentary approval, not trailed after Donald Trump".
Stop the War, a pacifist coalition once chaired by Corbyn, has called a demonstration outside the British parliament on Monday to protest about the strikes.
Former PM David Cameron, who lost a vote in 2013 on taking action in Syria, said Mrs May was right to take action.
But that doesn't mean people think the Syrian government wasn't responsible.
British opposition lawmakers are calling for Parliament to be given a vote before any military action.
Image Explosions in Hazeh in the rebel enclave of eastern Ghouta
British Prime Minister Theresa May is citing reports she says indicate the Syrian government used a barrel bomb to deliver the chemicals used in an attack on Douma. And while this action is specifically about deterring the Syrian Regime, it will also send a clear signal to anyone else who believes they can use chemical weapons with impunity.
Mrs May is reluctant to ask President Trump to hold off any action until she has the opportunity to consult MPs, the BBC understands from well-placed sources. This is the first time as Prime Minister that I have had to take the decision to commit our armed forces in combat - and it is not a decision I have taken lightly.
But after the Conservatives entered office in 2010, the government suggested that since the 2003 vote on Iraq, a convention had emerged that MPs should have a say, except in cases of emergency.
But the Cabinet's call for "action" to prevent further use of chemical weapons included no details on the method or timing of such strikes, while leaving open the possibility of other responses. The strikes at 0100 GMT were 15 miles (24 kilometres) west of Homs.
Following a discussion, Cabinet agreed it was vital that the "use of chemical weapons did not go unchallenged".
Vince Cable, leader of the Liberal Democrats, the fourth-biggest party in parliament, accused May of "riding the coat-tails of an erratic United States president".
"We should all be outraged at these horrific reports and images from Douma", Peter Salama, WHO Deputy Director-General for Emergency Preparedness and Response said, referreing to reports from the agency's health cluster partners - a WHO-led team of 118 national and global nongovernmental organizations, United Nations agencies, national authorities and donors working inside Syria to provide emergency and trauma care, as well as basic health services.
DUP leader Arlene Foster said the airstrikes were "limited but proportionate and justified".
It's Business as Usual for Syria's Assad After US-Led Attacks
And far-right figures Mike Cernovich and Laura Loomer also ripped Trump over the military strike in Syria. He called on Moscow to change course and join the West in seeking a more responsible regime in Damascus .