The Sudanese authorities are "careful" with foreign press. And – returning the favour – we are fastidiously careful back.

Visas to enter, a permit to be there, a third to practise the job. A licence for camera equipment and a Ministry of Information "meeter-&-greeter" at the airport to expedite its thorough inspection.

Then you apply for another permit to fly south to the areas controlled by the GOSS – Government of Southern Sudan – and, after a day or two, the Khartoum government office usually says: "Yes". 

And you get a generous glass of sweet tea while the paperwork passes from desk to desk.

It wasn't always like this.

Filming or writing about the fighting in the south could get you blacklisted by Khartoum. But these days the southern struggle is internationally legitimised, and the country poised on the brink of a messy and very public divorce.

Khartoum seems to be resigned to the world's curiosity. And the ministries facilitate your trip. 

But until those permits come through, Volkan the cameraman and I are in barely-operational mode.

"Don't even think about taking your TV camera to film on the street yet", advised a smiling ministry official," ... or you will get into trouble".

So when we heard the local dervishes were holding their regular Friday celebration in the oldest part of Khartoum, Omdurman, it was mobile-phone cams only in the bag, and off to a vast dun-coloured public cemetery on the outskirts.

Five o'clock in the evening, and the expanse was bathed in golden light. Two men had begun picking out a rhythm on tambors (WATCH VIDEO HERE).

Dervishes. We have those in Turkey, where we are based, and elegant and carefully-choreographed they are too. So what are dervishes doing in Khartoum? Could there be a Turkish connection?

Well, maybe ... maybe not. A learned and bespectacled local called Adil appeared at my side in the gathering crowd and when – after the usual pleasantries – he discovered we had flown in from Istanbul, told us that dervishes had arrived in Sudan with the Ottoman empire.

I'm not so sure – my subsequent reading suggests Sufism made it to Sudan from Arabia in the 16th Century. The Ottomans took another three centuries.

And this Dervish order could not have been anything but Sudanese in its spontaneity, diversity – and its fine rhythm.

The tambors had been joined by more drums, some simple instruments and a melodious chant of "There is no God but Allah". 

All ages and ethnicities, with some of the finest moves coming from grey-haired men old enough to be great-grandfathers.

Smiling, laughing. Some wore the flowing white local galibeyeh and imma (turbans), others a long green belted robe - "in celebration of nature", said Adil - and an array of colourful hats. One man even sported a head of dreads.

"People come here from all walks of life and cultural backgrounds", Adil explained. "It's irrespective of social identifications and ethnic groups. One of the benefits of the Sufi in Sudan is that it unifies people”.

At around this point, a persistent nasal declamation from a distant loudhailer intruded on the festivities. I could see the red pulse of police car lights behind the crowd of spectators.

"What's going on?" I ask. "Ah," Adil replies, "that's a demonstration by Ansar al-Sunnah. They are anti-Sufi – they don't approve of them.

"But they are out on the street - they are not allowed to come into the cemetery to protest. If they did, there would be a confrontation. The police will not allow this."

That's fortunate, because small children have joined the dervishes in their celebrations, and the crowd of spectators has swelled appreciably, swaying to the rhythm.

This particular Dervish order was founded by Sheikh Hamad el Nil, now buried under the nearby mosque, with his extended family under neighbouring tombs – colourful pastel monuments amidst the modest dun mounds of the rest of the graveyard.

A rich and distinctive fragrance fills the evening air. It's frankincense, which I last smelt in this concentration in a Greek Orthodox church.

Volkan is equally surprised. It's a strange moment of devotional crossover. A Dervish with a wood and metal censor walks past, shaking out thick clouds of incense.

He stops by me, and gives me an extra puff. "This is so you become a Muslim", explains Adil.

"Allah is alive!" chant the Dervishes, exultantly.

A young man next to me is watching on, smiling quietly. I ask him where he's from, and he tells me the Nuba Mountains.

That's in the middle of Sudan, along the disputed border, where the troubled relationship of North and South Sudan could once again turn violent. His name is Sadi.

"This is my addiction, my celebration," he tells me, gesturing at the dervishes. "I come here every Friday – it makes me very happy".

He grew up in this neighbourhood of Omdurman, on the other side of the Nile from Khartoum.

There is a possibility that if the referendum on Southern independence on January 9 provokes a "hard" partition, people like Sadi will be expelled back South, whether they want to leave or not.   

As the sun sets over the cemetery, the dervishes reach a final sustained and jubilant tempo, then stop for prayers.

Some of them just stop, lying flat on the ground in a trance-like state, in the embrace of spiritual ecstasy.

There are several million Sufis in Sudan. Their communing with the divine is said by some to have been influenced by early Christian and Hindu mystics.

Less than 10 per cent of Sudan's southern people are Christian – far more are animists, a form of nature-based mysticism. 

Perhaps there's a little something in tonight's celebrations for everyone.

The police and Ansar al-Sunnah have gone. The booksellers and coffee-stalls are packing up. We take our leave in the still, warm evening air where the finest frankincense I have ever inhaled hangs in a haze over us all.