Major General Chris Ghika, Deputy Commander of the Global Coalition’s joint task force, said the terror organisation is by no means “leaderless or rudderless”, despite its loss of physical territory.
But he said he could not predict whether the fall of the physical territory would substantially increase or decrease the terror risk to the UK.
The capture of Baghouz is a milestone in the four-year campaign to defeat the group’s self-described “caliphate” that once covered a vast territory straddling both Syria and Iraq.
It was announced on Saturday by Mustafa Bali, from the Syrian Democratic Forces, who tweeted: “Syrian Democratic Forces declare total elimination of so-called caliphate and %100 territorial defeat of Isis.
“On this unique day, we commemorate thousands of martyrs whose efforts made the victory possible. #SDFDefeatedISIS”
The US withdrawal is already underway, with its main ally, the Kurdish-led Syrian Democratic Forces warning that leaving too soon could have dangerous repercussions and a destabilising effect on the region.
Maj Gen Ghika told reporters at a Ministry of Defence briefing ahead of Baghouz’s fall: “There are no plans to scale down the contribution to Operation Shader.”
He added: “The US have said they are going to keep a presence in northern Syria so air power will play an important part in that, and we expect the British contribution to keep going on that side.
“In Iraq exactly the same maxim applies, the British troops that are training the Iraqi security forces are going to stay and keep doing what they are doing... because Isis continues to present a threat and that threat is met largely by the Iraqi security forces.”
Maj Gen Ghika said the coalition must remain “very conscious” about the continued threat of IS and warned against allowing Syria to become a “safe haven” for the ideology.
He continued: “They are not leaderless or rudderless. One of the reasons why even after the end of the physical caliphate ISIS will remain a dangerous organisation is because there are members of the organisation willing to take on the struggle.
“They are less experienced, they are less capable...than the people of years ago... so the organisation is weaker but there are still people willing to take on the leadership function...and that is one of the things that we target.”
Maj Gen Ghika estimated there were a few hundred IS fighters in eastern Syria, and between 1-2,000 in Iraq.
The SDF is holding more than 1,000 foreign suspected fighters in prisons that it runs in northern Syria.
The military commander said it was a “sovereign national decision” for countries on whether take back citizens who joined IS.
He said the British Government must decide whether British forces will have a role in repatriating citizens, including children of fighters.
Asked if the threat to the UK would be removed by keeping fighters imprisoned, he said: “I don’t think it removes it, but I think it reduces the threat of people of British origin who have fought with IS returning to the UK to conduct terrorist attacks”.
Maj Gen Ghika was also asked about whether the MoD will attempt to gather evidence from the battlefield once fighting is over which could be used to prosecute British fighters.
He said: “I think that’s too early to say whether that’s going to be possible but I think if we found any individual of any nation and we were able to link them to crimes and with evidence we have then we would expect them to be prosecuted under the force of the law.”