No fan of Britain's "special relationship" with the United States, the new left-wing leader of the country's main opposition party is against Prime Minister David Cameron's drive to join Washington's airstrikes on Syria.

But Jeremy Corbyn's position is out of step with some in his Labour Party, and Cameron will hope to poach opposition members if he asks parliament to authorize the extension of Britain's military action against the Islamic State group (IS) to Syria from Iraq.

That could be something that Corbyn, a veteran antiwar campaigner who has argued that Britain should leave NATO and has cast militant groups in the Middle East as friends, has to accept to avoid a damaging and acrimonious split in his party.