In early June, the British Islamic State member Sally Jones joined an exodus of jihadists from Raqqa as Kurdish and Arab forces closed in on the once impregnable capital of the terror group’s so-called caliphate.

With her on the long march were foreigners and their families who had been based in Raqqa throughout Isis’s meteoric rise and then bloody decline. Many had arrived at the height of its powers from mid-2014. Less than three years later they were engaged in an ignominious retreat.

During her years with Isis, Jones, dubbed “the white widow”, had become one of the group’s most senior females, given the job of indoctrinating other women, as part of the Anwar al-Awlaki brigades, and sending some on suicide missions. Killing her had been a priority of both US and UK intelligence, which had painstakingly tried to dismantle the group’s external operations capacity which was tasked with carrying out attacks abroad.

On the run, along with thousands of other foreigners, she was finally tracked to near the Syrian border. Washington and London are confident, but not certain, that Jones was killed. The fate of her 12-year-old son, Jojo, remains unclear. If her death is confirmed, Jones would join a handful of other British nationals killed in drone strikes. Her husband, Junaid Hussein, believed to be the head of Isis’s digital security unit, was killed near Raqqa in mid-2015. Ruhul Amin, from Aberdeen, and Reyaad Khan, from Cardiff, have also been killed by drones in the past two years.

With Raqqa now thought to be around two weeks away from completely falling to Kurdish and Arab forces, the ranks of Isis’s most hardcore foreigners have been steadily disintegrating. Another Briton, Jack Letts – dubbed “Jihadi Jack” – was captured in the deserts north of Raqqa in the summer. He, like dozens of other foreigners, remains in Kurdish captivity in north-eastern Syria. Further east, drone strikes and special forces operations have intensified as what remains of Isis’s organised elements tries to regroup in both Deir Azzour and Mayedin.

A journey to the Turkish border, which up to 271 French members of Isis have mostly used to get back to France over the past two years, now costs $20,000 a person – almost 10 times what smugglers were charging for the same journey a year ago. Dozens of Isis members, including senior officials, are known to have paid the price, with many making it as far as Idlib in northern Syria, but they are unable to cross the frontier.

In Deir Azzour, which remains besieged by a mixture of US-backed Kurds and Arabs, Russian special forces, Iranian-backed militias, including Hezbollah, and some Syrian regime units, up to 375 ideologically committed foreigners are thought to remain. Intelligence officials estimate that around half are French speaking – from Tunisia, Morocco, Algeria or France itself.

Iraqi officials believe that more than 30 British Isis diehards have made it to Mayedin, where the group’s senior leaders have also taken refuge. Some of the foreign fighters have also moved to Bukamal on the Syrian/Iraqi border. Yet more have attempted to blend in with refugees now fleeing Deir Azzour and Karama, near Raqqa.

“They don’t get far. We find them quickly,” said Mustafa Bali, head of military communications for the Syrian Democratic Forces (the US-backed umbrella group of Kurds and Arabs). “They are captured and sent to the intelligence people.”

In what remains of Isis-held Raqqa, around five square kilometres in the far south of the city, a string of desertions in the past week have allowed Kurdish-led groups to make rapid advances, including into the Clock Tower square in the east which had been emblematic of the organisation’s tyranny.

“The sniper’s alley was 400 metres, and it cleared quickly,” said Jamal, a Kurdish rebel in a telephone call on Thursday. Kurdish forces are planning to use the Clock Tower square to claim their victory in Raqqa, but first need to capture the hospital and sports stadium in the west of the city, which are both still in Isis hands.

Up to 1,000 civilians are thought to remain in areas that Isis still holds. Many are being used as human shields to prevent airstrikes. “They know that the planes won’t bomb if they see women and children,” said Elyas, a Kurdish officer at the east Raqqa frontline, last week. “If these people try to escape they often get shot. A few weeks ago there was an argument between the Syrian Isis members and the foreigners. The Syrians wanted to give up, but the foreigners wouldn’t let them. They all know it’s over.”

While the symbolism of the clock tower will offer a tangible sign of victory – the British executioner Mohammed Emwazi, known as “Jihadi John”, was killed there in 2015 – the sports stadium is considered to be of more intelligence value. The arena, which has been largely unscathed by airstrikes, was used to store weapons and plan attacks far beyond the fast-crumbling caliphate, particularly after the fall of al-Bab to Turkish-backed opposition groups this year. Attacks targeting France were thought to have been among those planned in the stadium by battle-hardened French ideologues and Iraqi veterans of the group.

“What is left of these guys now is something that we feel we can work with,” said a senior western diplomat. “What we don’t really know is how many of their kind have gotten to Europe and are ready or willing to act on instructions. We are confident though that we can stay on top of many, or most of them. They have limited means to communicate. They have less places to hide.”