We created the Syrian Refugee problem. Here's how to fix it.

The 70th UN General Assembly takes places this week and the most pressing issue facing world leaders as they gather remains ISIL and the crisis in Syria.

The issue is stark. ISIL is using deadly chemical weapons like Mustard agent. Every red line, of whatever width, has now been crossed.

If this is the existential threat and the battle of our generation, as the Prime Minister puts it, we do not appear to be doing much about it. It seems pretty clear after three attacks in Iraq and three in Syria that ISIL has significant quantities of Mustard agent, a deadly Class 1 chemical weapon.

This represents a major escalation in ISIL's terror campaign and physiological warfare. Mustard agent is a prescribed chemical under the Chemical Weapons Convention (CWC), is a blister agent, persistent, and highly toxic. The last two properties are the most worrying, especially in Syria where doctors and civilians have virtually no equipment and little knowledge to deal with the effects of this type of attack.

Initial reports from the attack on Merea indicated that it was a chlorine attack. But it wasn’t. Hence, when first-responders and doctors entered into these highly contaminated areas to treat casualties they became victims themselves. In some places, the Mustard agent in Merea could remain toxic for weeks. Perversely and axiomatically, I am now advising doctors and first-responders to decontaminate with chlorine at 0.5%, a chemical highly available in Syria.

Now that ISIL undoubtedly has Mustard agent, the main concern is how much have they got, and where did it came from? To take the latter first there are three possibilities:

1. They made it themselves – this is a possibility as the constituent chemicals are available in Syria and Iraq to do this. If proven, this would be a game changer.

2. It came from the Al Muthana Stockpile where Saddam Hussein’s chemical weapons are stored – This is unlikely but possible as ISIL had control between July – November 2014.

3. It came from Assad's stockpile – This is perhaps the most likely explanation. Many, including myself, believed there was up to 200 tonnes of Mustard agent missing from Assad’s chemical declaration to the UN in Oct 2013. The CIA recently stated that Assad still had some Mustard agent and the deadly VX and there is enough reporting to suggest that some fell into the hands of ISIL last December.

Therefore, if you accept the last thesis, ISIL could still have considerable amounts of Mustard agent and may have the capability to make more. This signifies a considerable step up of ISIL's terror campaign and one wonders where they might go to next. Of course any hint that part of this deadly chemical weapon arsenal is moved out of the Iraq/Syria theatre of war could have a very significant psychological impact regionally and globally.

There is not a moment to be lost. The UK, with its allies in the International Military Coalition, must step up the fight against ISIL and press to remove Assad in order create a liveable environment for civilians back in Syria.

We must create a No Fly Zone to prevent the haemorrhaging of civilians out of Syria, closely followed by Safe Zones to allow aid in. This will set the conditions to allow Syrians to get back into Syria. This will be cost effective, and morally far better for Syria. In conjunction with this, the International Military Coalition must step up its air and land campaign and hit, very hard, any ISIL units likely to possess or about to use chemical weapons.

The refugee problem in Europe is of our own making, a direct result of our inactivity towards Syria. If we allow this latest red line to remain crossed, it will not be one million looking for homes in the UK, Europe and the Middle East, but more like five million, and by the end of this year. And every single one of them would prefer to be in Syria. We must enable Syria to be liveable again for its people. Hamish de Bretton-Gordon is speaking on ‘Being Resilient to Terrorism: CBRN Hardening of Cities’ at the Global Resilience Summit on October 15th.