Britain's parliament backed a motion on Thursday requiring Prime Minister David Cameron to give it a veto over any future move to arm Syrian rebels, in a symbolic vote the government said it would heed.
Britain says it has not yet taken any decision to arm rebels fighting to topple President Bashar al-Assad, but its role in helping to lift a European Union arms embargo on Syria in May fuelled speculation it was planning to do just that.
The lower house of parliament voted by 114-1 to back a motion requiring the government to seek its "explicit prior consent" for any future decision to provide lethal assistance.
Though symbolic, the move is significant as it means Cameron will find it almost impossible not to give parliament a vote on the issue, something government sources say would amount to an effective veto over any decision to supply arms.
Ministers expect the 650-member lower house to vote against sending arms if the issue arises, said one government source.
Many lawmakers in Cameron's Conservative Party say they are worried a decision to arm the moderate opposition in Syria would escalate and widen the conflict and risk weapons falling into the hands of Islamist extremists.
"The government has discussed the option of arming the rebels. This would be a major policy change. This debate allows us to mark the government's card," said John Baron, a Conservative lawmaker who secured Thursday's vote.
The uprising led by Syria's Sunni Muslim majority is increasingly rallying around Islamist appeals as Assad's forces notch up battlefield gains against the rebels in a conflict that has killed more than 100,000 people since 2011.