Prime Minister David Cameron's hope that Britain would join air strikes against Islamic State group targets in Syria is fading due to the likely election of anti-war campaigner Jeremy Corbyn as leader of the opposition Labour Party.
After parliament returns on Monday, Cameron's government had hoped to call a vote on the issue in a bid to extend Britain's current role in coalition air strikes against IS targets in Iraq.
But Corbyn, a leading opponent to the 2003 Iraq war who wants to apologise over the conflict if elected leader of Britain's main opposition party on September 12, is deeply opposed to the move.
"I will only proceed going further on this issue if there is genuine consensus in the United Kingdom about it before going back to parliament," Cameron said during a press conference on Friday.
Cameron stressed that military action against IS was part of the "comprehensive program" he envisages to tackle the migrants crisis which has resulted in thousands of people, including many Syrians, flocking to Europe.
MPs in parliament's foreign affairs committee are due to discuss possible air strikes on Tuesday.
The prime minister cannot secure the necessary parliamentary approval for air strikes without opposition support due to a slim parliamentary majority and the opposition of some of his own MPs.
"He thinks there is a case for taking further action against ISIL (another term for IS) but he would prefer to proceed in a consensual way," Cameron's spokeswoman told reporters recently.
This looks impossible under a Corbyn leadership.
"I'm not convinced that air strikes in Syria will do any good other than kill a lot of civilians and other people," Corbyn said at a campaign event last week.
Cameron's government was defeated on taking military action in Syria in 2013 in one of the most damaging foreign policy blows to his previous coalition government.
If Corbyn is elected Labour leader as expected, it could also pose wider and highly sensitive problems on defence for Cameron.
Asked if there were any circumstances under which he would deploy military forces abroad during a debate on Thursday, Corbyn said: "I'm sure there are some. But I can't think of them at the moment."
Corbyn, who was a leading figure in the Stop The War Coalition, which organised one of Britain's biggest ever rallies against the Iraq conflict in 2003, also wants to scrap Britain's nuclear deterrent.