Then it was a question of striking at President Assad's forces as punishment for his use of chemical weapons. In the event the government lost the vote and no bombing occurred.

Since then the Islamic State organisation has emerged, controlling what it describes as a caliphate, encompassing territory in both Iraq and Syria.

IS has also demonstrated its ability to carry out or inspire attacks against tourists in Tunisia, against a Russian airliner over Egypt, and against a variety of targets on the streets of Paris.

A broad coalition (including the UK) is carrying out air strikes against IS in Iraq and a smaller number of countries are hitting targets in Syria too. (RAF aircraft are conducting intelligence-gathering missions over Syria, but generally not releasing any weapons.)
Media caption David Cameron on IS: "They have already tried to attack us"

Mr Cameron went to the House of Commons on Thursday to set out the government's case for extending air strikes into Syria.

    Eleven key questions on Syria answered

He clearly believes that this is the right thing to do, that Britain's participation wasn't just essential alongside its key allies, but that it would also make a difference to the campaign. And furthermore, he believes that a reinforced military effort would bolster diplomatic efforts to end the Syrian crisis and increase the chances of a comprehensive settlement.