The solution is not opening up Europe’s borders; it’s defeating ISIL and removing Assad from power.

Europe and the Middle East are looking at a million refugees needing help today. This figure could easily escalate to five million by the end of the year, unless there is a significant policy shift by the international community towards Syria.

But are we missing the point about opening our doors to Syrian refugees? Surely we must set the conditions to allow them to return as soon as possible to their homes in Syria?

Listening to news media today demanding that the UK government and others open their doors to thousands of Syrian refugees strikes me as the completely wrong approach – and illustrates that we really haven’t learned lessons from Iraq and Afghanistan.

I’ve been to Syria a bit in the last four years and to Iraq and Afghanistan a lot over the last 25 years. I know many Syrians; every single one wants to return to Syria.

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The refugee problem in Europe is of our own making. It is a direct result of our inactivity towards Syria hitherto, and particular, us ignoring the perceived and stated red lines on the use of chemical weapons after the Ghouta chemical attack in August 2013, which killed up to 1,500 people.

Back to Syria

We must create “safe zones” and a no-fly zone now in order to get Syrians back into Syria. This will be better for the Syrian people; it will be cost effective and morally far better for Syria than allowing potentially five million Syrian refugees into Europe and the Middle East.

The UK, with its allies in the international military coalition, must step up the fight against the Islamic State of Iraq and the Levant (ISIL) and press to remove Bashar al-Assad from Syria in order to create a liveable environment for civilians in Syria.

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ISIL is now using deadly chemical weapons, like mustard gas. This must be the last straw – now with every red line of whatever diameter now crossed. Some advocate prevarication to allow the Chilcot Enquiry on Iraq to be published. Presumably, this is to ensure that we do not make the same mistake as the 2003 invasion of Iraq.

But from personal experience, I can say unequivocally that Iraq 2003 and Syria 2015 are completely different situations. For one, we didn’t have millions of refugees in 2003, though there were other terrible issues that we did have in Iraq.

The UK, with its allies in the international military coalition, must step up the fight against ISIL and press to remove Bashar al-Assad from Syria in order to create a liveable environment for civilians back in Syria.

There is not a second to be lost, and the UK could have made this decision to attack ISIL in Syria back in July when Michael Fallon, the UK defence minister, first suggested it.

If this is the existential threat and the battle of our generation, as Prime Minister David Cameron put it, we do not appear to be doing much about it.

It seems pretty clear now after three attacks in Iraq and three in Syria in the past ten days that ISIL has significant quantities of the deadly “Class 1” chemical agent, mustard gas.

Attacks against Peshmerga forces near Erbil have been confirmed as mustard agent, and the attack on Marea, the strategic town between Aleppo and the Turkish border, is also almost certainly mustard gas.

Psychological warfare

This represents a major escalation in the ISIL terror campaign and psychological warfare on those who oppose them.

Mustard agent is a prescribed chemical under the Chemical Weapons Convention (CWC) and 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 on how to deal with the effects of a mustard attack. This has been personified by the actions after the Marea attack.

Until recently, Assad had been dropping chlorine barrel bombs on Aleppo. Chlorine is not very toxic and very non-persistent, dispersing in minutes. Initial reports from Marea were that this was a chlorine attack, but it wasn’t.

Hence, the first responders and doctors went into highly contaminated areas to treat casualties and became victims themselves. The mustard in Marea could remain toxic for weeks in some places.

A Syrian kid receives treatment at a field hospital following a suspected chlorine gas attack [GETTY]

Now that ISIL undoubtedly has mustard agent, the main concern is how much have they got, and a lesser issue of where it came from. To take the latter first, there are three possibilities:

They made it themselves – possible, as there are probably all the constituent chemicals available in Syria and Iraq to do this. This would be a game change if proven.

Or, it came from the Muthanna stockpile, where Saddam Hussein’s chemical weapons are stored and which ISIL controlled from July to November 2014; unlikely, but possible.

Or most likely, it came from Assad’s stockpile. Many, including myself, believe there was up to 200 tonnes of mustard agent missing from Assad’s chemical declaration to the UN in 2013.

The CIA recently stated that Assad still had some mustard agent and the deadly VX nerve agent, and there is also enough reports to suggest that some had fallen into the hands of ISIL last December.

ISIL steps up campaign

Therefore, if you accept the last thesis, ISIL could still have considerable amounts of mustard agent and the capability to make more.

This signifies a considerable step up in ISIL’s terror campaign, and one wonders where they might go to next.

Of course, any hint that this deadly chemical weapon arsenal is moved out of the Iraqi and Syrian theatre of war could have a very significant psychological impact regionally and globally. But as we are helping doctors and first responders on the ground mitigate this threat in Syria, the same should apply outside of the warzone.

In sum, 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. 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 use chemical weapons.

This is a red line we absolutely cannot afford to ignore, and we must begin to set the conditions for Syrian refugees to return to Syria, or it will not be one million looking for homes in the UK, Europe and the Middle East, but more like five million, and as early as the end of this year.

Hamish de Bretton-Gordon is a chemical weapons adviser to NGOs working in Syria and Iraq. He is a former commanding officer of the UK Chemical, Biological, Radiological and Nuclear (CBRN) Regiment and NATO’s Rapid Reaction CBRN Battalion.

The views expressed in this article are the author’s own and do not necessarily reflect Al Jazeera’s editorial policy.