Andrew Day is a junior research fellow at the Henry Jackson Society.

The reported killing of Mohammed Emwazi – “Jihadi John” – raises once again the question of wider British action in Syria.

Earlier this week General Sir Nicholas Houghton, the Chief of the Defence Staff, warned that Britain was “letting down” its allies by not participating in airstrikes against Islamic State strongholds in that country.

His remarks came just after the Defence Secretary, Michael Fallon, told journalists that not tackling Islamic State in Syria was “morally indefensible”.

As Islamic State continues to hatch murderous terror plots against British citizens, it cannot be right for Britain to stand aside and leave the heavy lifting to its coalition partners.

Two years ago Britain opted out of responding to President Assad’s use of chemical weapons against civilians in opposition-controlled suburbs of Damascus.

Arguments about the unintended consequences of military intervention have been well rehearsed this past decade. Less often discussed are the dire humanitarian consequences of adopting non-interventionism as a matter of principle.

In Washington, President Obama’s “red lines” for action against the Assad regime were each rubbed out, out one by one, by a dictator who realised there would be no great consequence for this breach of international norms.

From this point onwards, the Syrian civil war intensified and the first half of 2014 saw Islamic State making rapid territorial gains across Syria and Iraq. From its new footholds in Syria and elsewhere, Islamic State is plotting murder against British citizens.

Back in June an Islamic State-linked gunman killed scores British holidaymakers in Tunisia. This was the most significant loss of British life in a single terrorist attack since 7/7.

Britain is currently dealing with a wave of terror plots, the highest number for thirty years, with the vast majority of these being directed or inspired by Islamic State.

Earlier this year British intelligence uncovered a plot to attack VJ Day commemoration services in London during August. The plot was orchestrated by Islamic State in al-Raqqa, northern Syria.

The Royal Air Force is already flying sorties against Islamic State targets in Iraq. To not extend these operations to Islamic State supply lines and command centres in northern Syria is the height of military confusion.

Islamic State butchers and enslaves people on both sides of the border. Our allies in the Global Coalition are already striking Islamic State over Syrian territory.

Whilst it is true that any British contribution would be relatively small in size compared to that of the United States, bringing RAF Tornadoes into the fold would provide coalition commanders with greater flexibility, and offer up an additional airbase in Cyprus.

Islamic State makes no secret of it pathological hatred of free societies. It wishes to impose a totalitarian death cult over as much territory as it possibly can. One of the weaker arguments put forward against targeting the group in Syria is that such action would fuel radicalisation.

That is to say, the terrorist is only terrorising us because the British behaved poorly towards him. The extremist is only extreme because we have shown him an intolerable level of intolerance.

Investigations into the background of the Tunisian gunman at Sousse actually revealed he was aggrieved, at least partially, by western inaction against Assad. Trying to identify ‘root causes’ is usually a futile task, but policies of non-interventionism have not spared Germany, Austria and Sweden from jihadist plots.

Any decision to shy away from confronting Islamic State will erode Britain’s moral authority and undermine its reputation as a steadfast ally. A non-committal approach will not go unnoticed in Washington, whose diplomats already quietly talk of a “Great Shrinking Britain.”

To be sure, there are no easy options in Syria, but MPs should guard against outsourcing British defence policy to pilots from the United States, France and Jordan. With Islamic State plotting to bring terror to the streets of western capitals, MPs should consider what signal walking away sends to traditional allies and regional partners.

The Prime Minister has spoken confidently of the need to defend liberal democracy and western values both home and abroad. Caught between the barrel bombs of the Assad regime and the barbarity of Islamic State, the people of Syria now need British MPs to take a stand.

The citizens of the United Kingdom also need their MPs to do the same.