UK strategy of not attacking Isis in Syria is illogical, says defence secretary

“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.”
The logic is that the Americans don't want to do anything on the Syrian side of the border that might upset Assad, like protecting Syrians from ISIS attacks, or God forbid, Assad's bombing. The logic is that Britain entirely supports the American strategy, it is only because this is becoming unsustainable for those countries most directly affected by this neglect and partiality, like Turkey, which is threatening to establish a buffer zone in Northern Syria* to protect Syrians from Assad and ISIS, and forestall the possibility that the Kurds will establish a state in Northern Syria, that Michael Fallon is expressing any doubts as to the direction they've taken.
*[http://eaworldview.com/2015/06/syria-daily-turkey-considers-intervention-with-air-operations-and-ground-troops/]