With momentum building over military action against Isis in Iraq and Syria, almost nothing has been said about what this might mean in humanitarian terms, such as population flows and new refugees.

In just a few short weeks Isis managed uproot 600,000 people in and around the Mosul region. Inhabitants of villages like Kocho and Qiniyeh were either massacred or managed to flee to the inhospitable terrain of Mount Sinjar. In a terrible twist of fate, many of these traumatised people have exchanged certain death in Iraq for the deep uncertainties and mortal dangers of Syria.

A new wave of attacks on Isis’s roving bands of killers will surely displace thousands more local residents. It’s hard to see how aerial assaults on militants — or even the prospect of mass attacks — can have any other effect. What plans has John R Allen, the retired US general charged with overseeing the anti-Isis drive, made for those caught in this new pincer movement?

I raise these matters having recently returned from Lebanon where I witnessed the plight of some of the 1.4 million Syrian refugees now living in the country. Consider that number for a moment. Lebanon had a pre-Syrian conflict population of around 5m people. It’s seen a gargantuan influx of more than a quarter of its entire resident population, equivalent to something like 16m refugees pitching up in the UK in the space of three years. And it isn’t stopping; Lebanon is still receiving 9,000 refugees a week from Syria.

The numbers are off the scale, and Lebanon is beginning to feel the strain. Despite the incredible hospitality and kindness of thousands of Lebanese people — some hosting distant relatives from across the Syrian border, many simply helping struggling strangers in their midst — the country is under unbelievable pressure.

Iraq crisis: Yazidi nightmare on Mount Sinjar Show all 15 1 /15 Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Displaced people from the minority Yazidi sect, fleeing violence from forces loyal to the Isis in Sinjar town, walk towards the Syrian border, on the outskirts of Sinjar mountain, near the Syrian border town of Elierbeh of Al-Hasakah Governorate Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Displaced people from the minority Yazidi sect, fleeing violence from forces loyal to the Isis in Sinjar town, walk towards the Syrian border, on the outskirts of Sinjar mountain, near the Syrian border town of Elierbeh of Al-Hasakah Governorate Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Displaced Iraqis from the Yazidi community settle at a camp at Derike, Syria. In the camps here, Iraqi refugees have new heroes: Syrian Kurdish fighters who battled militants to carve an escape route to tens of thousands trapped on a mountaintop Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis A pilot based at RAF Marham entering a Tornado GR4 prior to taking off for the reconnaissance mission over Iraq. Several RAF Tornado jets set off from RAF Marham in Norfolk this afternoon to travel to a "pre-position", from where they will fly to northern Iraq to provide improved surveillance of the situation on the ground. The jets, fitted with Litening III targeting and surveillance pods, will be able to fly over the crisis area to provide intelligence and help with the delivery of humanitarian aid Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis A British Royal Air Force (RAF) Tornado GR4 aircraft equipped with the Litening III pod from RAF Marham, eastern England, on their arrival at RAF Akrotiri Cyprus for their reconnaissance mission over Iraq Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Aid inside a Royal Air Force (RAF) Hercules C130 J aircraft before being airdropped to civilians in Iraq Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis A Royal Air Force (RAF) Hercules C130 J military transport plane at RAF Akrotiri in Cyprus. Britain made a third round of airdrops of supplies to aid refugees stranded on a mountain in northern Iraq, officials said, as Tornado fighters arrived at an RAF base in Cyprus preparing to provide surveillance support for the humanitarian effort Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Royal Air Force (RAF) Tornado GR4 aircraft, flown in from Britain, stand on the tarmac at RAF Akrotiri in Cyprus Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis A displaced man helps a woman, both from the minority Yazidi sect fleeing violence from forces loyal to the Isis in Sinjar town, as they make their way towards the Syrian border, on the outskirts of Sinjar mountain, near the Syrian border town of Elierbeh of Al-Hasakah Governorate Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Iraqis including Turkmen, Shabaks, Kurds, Yezidis and Christians, fleeing from assaults of army groups led by Isis, take shelter at Bahirka Camp in Arbil Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Displaced Iraqis from the Yazidi community look for clothes to wear among items provided by a charity organization at the Nowruz camp in Derike, Syria Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Displaced Iraqis from the Yazidi community gather for food at the Nowruz camp in Derike, Syria Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Displaced Iraqis from the Yazidi community gather for food at the Nowruz camp in Derike, Syria Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Syrian Kurdish Peshmerga fighters take a sick Iraqi Yazidi woman to the clinic at Nowruz camp in Derike, Syria Iraq crisis: Yazidi nightmare on Mount Sinjar Iraq crisis Sick displaced Iraqis from the Yazidi community wait for treatment at a clinic at Nowruz camp in Derike, Syria

Ninette Kelly, head of the UN refugee agency in Lebanon, told me that hundreds of thousands of Syrian refugees in Lebanon are living in informal settlements, and even in garages and shops. I visited a refugee settlement in the Bekaa Valley, a two-hour drive from Beirut. Here hundreds of people are huddled under plastic sheeting strung across wooden struts (these are not even tents), many living on the bare earth. They are all but exposed to the elements, contending with freezing winters and searingly hot summers. There are no kitchens, and the few toilets available are incredibly basic.

Healthcare is virtually non-existent. I met a mother who fears her five-month-old boy may be deaf and suffering from a serious eye condition, but she is unable to afford the treatment he needs. Another woman was caring for her mother, who has suffered three strokes, as well as her young, epileptic son. Again, the treatment they need is unavailable and unaffordable, but she also fears for the fate of two of her brothers who are languishing in Bashar al-Assad’s prisons. They will almost certainly have suffered tortured and she’s in anguish at the thought that they’ll be killed.

Existence itself is hard but so is co-existence. In Bekaa there have been disputes between refugees and the local Lebanese community over access to water. Is this surprising? Lebanon is small, not especially wealthy and is already hosting the largest population of Syrian refugees of any country in the world. No-one knows when the conflict in Syria is going to end, and in some quarters patience is running out.

Well over a year ago voices in the Lebanese government were saying the country had already “exceeded its ability to absorb” refugees, however desperate or deserving. Recently the atmosphere has become even more fraught after the beheading of two captured Lebanese soldiers, almost certainly by Isis. People say they’ve “woken up in a different world” after the beheadings, with anti-Syrian sentiments hardening and posters saying “No Syrian refugees here” appearing on the streets.

Syria is facing the world's biggest humanitarian crisis, and its neighbouring countries can’t manage on their own. Around the world, despite the politicians’ promises, the response has been woeful. EU countries have taken less than 1% of Syria’s refugees, the UK has resettled a grand total of 51 people.

As I left Lebanon a government adviser said to me “Don’t tell us to keep our borders open, while you close yours”. It’s a remark that ought to be reverberating around Downing Street as the generals explain to David Cameron how they’re going to “destroy” Syria’s Isis fighters.