Islamic State defectors who are "disillusioned" with the terror group could be used by the governments to deter potential fighters by providing them opportunity to speak out against the dreaded outfit, a British terrorism think tank said on Monday.

At least 58 people have left the group and publicly spoken about their defection since January 2014, a report by the International Centre for the Study of Radicalisation and Political Violence (ISCR) at King’s College London said.

‘Entitled Victims, Perpetrators, Assets: the Narrative of Islamic State Defectors’ says the governments should "provide defectors with opportunities to speak out, assist them in resettlement and ensure their safety and remove legal disincentives that prevent them from going public."

The ISCR says the 58 defectors are likely to represent a much larger group who have yet to come out publicly.

In August 2014, one Briton, who was too frightened to return to the UK and whom ICSR did not record as a public defector, told researcher Shiraz Maher, "Muslims are fighting Muslims… Assad’s forgotten about. The whole jihad was turned upside down."

Peter Neumann, ICSR director and the report’s author, said new legal frameworks had to be devised to support and encourage such defections.

"It seems to me to be wrong that if someone is helping to deter people to join ISIS by casting a negative light on the group, that he is then being punished for it," he told the ‘Guardian’.

"Right now, if you speak out, the prosecutor will say, ‘oh that’s very interesting, so he’s admitting membership of ISIS, so we can prosecute him for that.’ So that needs to stop. We are not asking for the creation of legal incentives, saying ‘if you tell a nice story you get an amnesty,’ but people right now are being actively punished for speaking out and I think that needs to change.

"Lawyers need to figure out a solution for that so people are no longer dis-incentivised for that," Neumann said.

The defections, although limited in overall numbers, "have been sufficiently frequent to shatter ISIS’ image as a united, cohesive and ideologically committed organisation," the report said, adding that the pace of public defections has increased in recent months as almost 60 percent of the cases were reported in the first eight months of 2015, 17 of which appeared this summer.

The main reason cited by the report for the disillusionment with ISIS centres around how "brutal ISIS is towards the very people they are pretending to protect, Sunni Muslims in the region."

Among other reasons for quitting include that ISIS is more interested in fighting fellow Sunni Muslim radicals, tribes and civil organisations than Syria’s Assad government, that it is "corrupt and un-Islamic" and that life under ISIS "is harsh and disappointing", the report said.