I stopped to buy walnuts in Sidon last week from a sunburned man sitting on the pavement of the old souk. Like the walnuts – soft, almost creamy inside their iron-hard husks – he came from the Syrian town of Bloudan.

In years gone by, I would take the steam train from the old Haj station in Damascus up to Bloudan and Zabadani, the loco so slow that passengers could sometimes jump out of the carriages to pick fruit and then clamber back aboard. Bloudan was a kind of forested spa, all soft-flowing streams and water melons and crude cement houses and big posters of Hafez al-Assad, the dictator father of Bashar. There were Palestinian training camps in these hills and a regional headquarters for the Iranian Revolutionary Guard – Lebanon was only eight miles away – and the smugglers’ trails ran from Bloudan and Zabadani across the Anti-Lebanon range into the Bekaa Valley.

Bloudan is a Christian town – Zabadani is largely Sunni – and they have been on the front lines of Syria’s war; those old smuggling trails now help to bring the tens of thousands of Syrian refugees into Lebanon, swelling now to 1.3 million, of whom at least 780,000 have been registered by the UN. This means that one in four of the people of Lebanon are now Syrians. It feels like it, too. The poor beg in the streets of Tripoli, Beirut, Sidon and Tyre, the rich cut in front of me in their smart cars with registration plates showing they come from as far away as Raqqa and Deir ex-Zour and Deraa. A few of the vehicles boast bullet holes – as so many Lebanese cars did during the 1975-90 civil war – and almost half the people I meet in an average day in Beirut are Syrians.

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They work on the building sites in the side street outside my home.

Two years ago they all supported Bashar. Then the poorer labourers proclaimed the Free Syrian Army as their heroes and the supervisors turned out to be pro-regime “mukhabarat” intelligence agents.

Now the rebel faction on the building sites is silent – no Islamists they – while the pseudo-cops keep their mouths shut. The wealthy Syrians have moved into swish apartments downtown. I sometimes find that when I travel from Beirut to Damascus at the weekend, half the Syrians I want to see are not in Damascus at all. They are spending the same weekend in Beirut.

There is cause for much shame in this massive influx of refugees. When the Lebanese fled to Syria during their civil war, they were treated with great care by the regime. Now the Lebanese resent the huddled masses from the east. They are beaten in the immigration queues, cheated with exorbitant rents and, in some towns (Christian, I am sorry to say), told to stay off the streets after 8pm.

Christian Palestinians from Damascus are living in penury in one-room shacks in the only Christian Palestinian refugee camp in Dbayeh. The Sunni Palestinians from Syria have fetched up in the hovels of Sabra and Chatila to exchange their stories of horror with the tales of massacre and savagery visited upon their Palestinian brothers and sisters of this forsaken Lebanese camp at the hands of Israel’s cruel allies 31 years ago.

And it’s not hard to see why Najib Mikati, the outgoing “ghost” Prime Minister in the equally ghostly Lebanese government, is now talking of “investigating” each Syrian arrival to discover if they meet “the legal conditions of a refugee” – whatever that is – and the implications are obvious: those who have arrived in Lebanon to gather support for the Damascus regime or for the Syrian resistance will be chucked out.

Easier said than done. Lebanese ex-general Michel Aoun’s crackpot and largely Christian “Free Patriotic Movement” wants the border closed; and since Mr Aoun supports Bashar al-Assad – and since most refugees in Lebanon are anti-Assad Sunni Muslims – you can see why Mr Aoun wants the frontier blocked.

But there are deeper concerns, which afflict both the Lebanese army and the Internal Security Force, the only two viable institutions in Lebanon: that the great refugee camps spreading down the Bekaa valley might turn into miniature Ein el-Helwehs.

Ein el-Helweh is the vast Palestinian camp in Sidon whose 100,000 (or more) refugees are crammed into slums controlled by armed Palestinian militias which operate outside the law of Lebanon. Subjected to the country’s oppressive work restrictions, the Palestinian factions include Hamas and the PLO – but also Islamists, a faction of al-Qa’ida and members of Muslim groups wanted for their part in a Salafist insurrection in northern Lebanon six years ago.

A cancer in the body politic, as far as Lebanon is concerned; a pit of hopelessness for the 100,000 whose lands in Palestine were seized by the new Israeli state in 1948.

But the Lebanese army now fears that the blossoming Syrian camps in the Bekaa will yield the same, bitter fruit: armed groups supporting both the impoverished Free Syrian Army and the ever-more-powerful Sunni Muslim al-Nusra front and al-Qa’ida affiliates who are fighting to “liberate” Syria from Assad’s government.

The Lebanese cannot afford to let the cities of Syrian refugee tents turn into armed camps outside the sovereignty of Lebanon, run by Syrians carrying their own weapons outside the law.

But can the Lebanese prevent this infection when Syrian suffering is on such a scale? On Saturday night I found three Syrians – two of them only 14 years old – selling white roses on the Beirut Corniche near my home.

Amir came from the Damascus suburb of Douma a year ago. His right leg had been torn off by a shell. Hadi and Hani were brothers from Hama. Hadi’s hand had been amputated by a shell fragment eight months ago. Only Hani was untouched. I bought a white rose. Three Syrians, only one complete.

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