Britain says it has not yet taken any decision to arm the foreign - backed insurgents fighting Syria government, but its role in helping to lift a European Union arms embargo on Syria in May fueled speculation it was planning to do just that.
The lower house of parliament on Thursday 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.
Crisis in Syria started in March 2011, when pro - reform protests turned into a massive insurgency following the intervention of Western and regional states.
The unrest, which took in terrorist groups from across Europe, the Middle East and North Africa, has transpired as one of the bloodiest conflicts in recent history.
As the foreign - backed insurgency in Syria continues without an end in sight, the US government boosts its political and military support to Takfiri extremists.
Washington has remained indifferent about warnings by Russia and other world powers about the consequences of arming militant groups.