Ghadi had spent the past two years on the run from the Syrian regime but it was the rebels fighting against the government, the so-called Free Syrian Army (FSA) who finally caused him to abandon the revolution and flee Damascus. He had made the mistake of speaking out against one of the big FSA brigades running the Yarmouk district of the capital. ‘They are thieves and gangsters,’ he told me. ‘One Facebook post about what they’re doing will get you killed.’

I met Ghadi in a Beirut café, after he had made the long trek over the mountains from Syria to Beirut. Other activists joined us, all bitterly disillusioned by the corruption, looting and kidnapping that has consumed the uprising. When FSA fighters in Yarmouk had car trouble, they said, they would casually set up a checkpoint to seize another vehicle ‘for the revolution’. Mercedes were popular.

Ghadi, a tall young man of about 30, had helped to run a centre collecting food for refugees. But FSA fighters arrived, and without apology or explanation piled the food into a pick-up truck and drove off. This was the final straw for Ghadi, but he’d had doubts about the ‘resistance’ for months.

As a ‘citizen journalist’, he followed the FSA, camera in hand. One day the local commander led him down into a basement and said: ‘Look at this.’ Ghadi’s video shows five men sitting, all rigid with fear, stripped to the waist, blindfolded, hands bound behind their backs. Ugly bruises cover most of their upper bodies. They had been seized from a suburb loyal to the government. They included a clerk in the foreign ministry, a new recruit to an artillery regiment and a secondary school headmaster.

The headmaster’s dignity had long gone, his comb-over pointing in all directions. The commander smoothed the wisps of hair. The man shrank like a beaten dog. ‘Haven’t we treated you well?’ said the commander. Then he kicked him under the chin, snapping his head back. ‘These are all spies,’ he declared.

By the standards of Syrian atrocity videos, this was more creepy than shocking. But what had upset Ghadi was that the commander wasn’t at all worried he was filming — he wanted him to show the basement.

Speaking out was not a popular move. ‘People are always telling you, “It’s not the time to talk about what’s going wrong; it’s the time to fight the regime”,’ said Ghadi. ‘But I believe that if you truly want to fight Bashar, you must correct what the FSA is doing on the ground. I feel so angry. I am not asking for a revolution that’s 100 per cent clean and pure. But the FSA brigades in Damascus are not fighting for freedom any more. The FSA has lost the trust of the people.’

‘This is the Department of Abu Qatada.’

‘This is the Department of Abu Qatada.’

These men I met were all secular activists and one of their great worries was about the increasing power of the main jihadist group, Jabhat al Nusra, or the Nusra Front. A Jabhat fighter once strode into their media centre, said Ghadi, and found an old vodka bottle that had water in it. The fighter flung the bottle to the ground, shattering it, and crying out: ‘God is great!’ Ghadi told him: ‘Save “God is great” for when you blow up a tank or shoot down a jet — not for smashing a bottle.’

Jabhat al Nusra only emerged in January last year and for a long time they were a secretive and apparently small group, posting videos of suicide bombings. Now they are everywhere, their ranks swollen by young Syrians impressed by their discipline and piety and by foreigners looking for a holy war, wherever it might be.

Last month, the Nusra Front detained four Italian journalists in the northern province of Latakia. Among them was a friend of mine, Susan Dabbous, a Syrian-Italian correspondent. The journalists were filming inside a desecrated church in a formerly Christian village, the Christians having fled when the Nusra Front arrived. They faced the customary accusation of spying, by a group that was led by a 28-year-old ‘emir’.

At times, said Susan, the ‘emir’ really seemed to believe he had captured four dangerous western agents. He was Syrian but the fighters included Tunisians, Moroccans, Saudis. They were itching to kill a westerner, firing over the journalists’ heads with their Kalashnikovs. ‘Why are you helping the kafirs [infidels]?’ the emir asked the journalists’ Syrian fixer. He alternately tried to convert Susan to Islam and threatened to cut her hands off. ‘I know you are compiling a dossier on me,’ he told her. Halfway through their captivity, the jihadis started celebrating as it was announced that the Nusra Front had formally joined al-Qa’eda.

Not everyone was celebrating: there have been protests against the Nusra Front because regular Syrians don’t want a Taleban telling women to wear the niqab and not to drive, and the Nusra Front is involved in a vicious feud with elements of the FSA. This is partly over spoils, partly ideological. Elsewhere, however, the FSA is so close to Nusra it has almost fused with it. Some of the most powerful FSA brigades have dispensed with the language of democracy and are now talking unambiguously about waging a war to impose sharia law.

On my last trip into Syria, I met Ayat, a female activist who had worked in a Damascus bank before she turned to running guns for the revolution. In tight black jeans and sneakers, she still looked like the girl-about-town she had once been. She refused to cover up in a hijab and would not leave the room when the men arrived, however much the fighters hissed at her and told her (literally) to get back to the kitchen. Ayat was in despair about the FSA’s inability to take the capital. ‘Each group is just sitting on its weapons trying to grab what they can for themselves,’ she said. Things are getting so bad, there are even reports of rebel fighters defecting back to the government side, disgusted with the way the armed uprising has betrayed its ideals.

Ayat’s husband, a law student before the uprising, commands an FSA unit generally regarded as honest, so there do still exist rebels untainted by corruption. But they are few and far between, and identifying them becomes harder all the time.

Paul Wood is a BBC Middle East correspondent covering Syria.

This article first appeared in the print edition of The Spectator magazine, dated