Britain has taken a step further towards expanding its aerial bombing of Islamic State forces beyond Iraq to targets in Syria after the defence secretary, Michael Fallon, described the current strategy as illogical.

In a sign that David Cameron is keen to explore parliament’s readiness for a widening of the campaign, Fallon said that MPs needed to think very carefully about how to defeat an organisation that ignores international borders.

The defence secretary told The World at One on BBC Radio 4: “We’ve always been clear that Isil [Isis] has to be defeated in both Syria and Iraq. We have plenty to do in Iraq. Each member of the coalition is doing different things. Isil is organised and directed and administered from Syria. There is an illogicality about not being able to do it.”

The prime minister is keen to explore whether the newly elected parliament would support an expansion of the bombing campaign as part of what he describes as his “full spectrum” response to Isis in light of the Tunisia gun attack. Cameron won parliament’s support last year for the air strikes against Isis targets in Iraq.

But the prime minister stopped short of trying to win approval for expanding the air strikes to targets in Syria amid objections from the Labour party. Cameron was defeated in August 2013 when Ed Miliband effectively blocked military strikes against the regime of Bashar al-Assad after a chemical weapons attack near Damascus.

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Cameron, who is due to outline his response to the Isis threat abroad and to the extremist threat at home within weeks, wants to test the waters for a renewed parliamentary vote to permit air strikes on targets in Syria.

In what is being described a “pitch-rolling” – the buzz-phrase for the process of preparing the ground for a change in strategy – the prime minister will see if it is realistic to return to the Commons for a vote in the autumn after the election of a new Labour leader. Cameron will be unable to act without the support of the Labour frontbench because Tory rebels would cut his parliamentary majority on any military action.



Fallon said: “It is a new parliament and MPs will want to think very carefully about how we best deal with Isil. [There is an] illogicality [with] Isil not respecting the border lines; they don’t differentiate between Syria and Iraq, they’re establishing this evil caliphate across both countries. There is no legal bar to us operating in Syria but we don’t have the parliamentary approval for it.

“We don’t need it at the moment because we are playing our part in the campaign and what we do in Iraq actually frees up the US aircraft to attack in Syria. Isil has to be defeated in both countries. Its evil in Iraq is all being directed by its headquarters in Syria.”

Fallon suggested that proof of a direct link between the Tunisian gun attack and Isil would intensify calls for striking targets in Syria. He said: “If we can link it back, [if] it does link directly back to Isil in Syria then we will have to reflect with the rest of the coalition how best we deal with that.”

The prime minister’s spokeswoman said: “The prime minister has been clear on the need for us to be crushing Isil in both Iraq and Syria in the sense of the role we are playing alongside others.

“Clearly Isil is seeking to find areas from which it can operate, from which it can seek to threaten people here in Britain. As part of what the PM was talking about, in terms of having a full-spectrum response, that means not just focusing on one area where they are but looking at a whole range of areas and how Isil are operating.”

