A disillusioned Islamic State fighter has reportedly leaked the private information of 22,000 terror recruits to journalists — including at least one alleged Australian member.

The potentially highly valuable trove of data was given in a memory stick to Sky News by an IS defector, the media company reported on Thursday.

Intelligence agencies have begun a process of verifying the digital files, which reportedly contain addresses, telephone numbers and family contacts of people who joined IS.

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One of the unconfirmed identities is an Australian engineer aged 36 using the codename Abu Oubeida Al Loubnani.

A former head of spy agency MI6, Richard Barrett, said the data was “an absolute goldmine”.

“It will be an absolute goldmine of information of enormous significance and interest to very many people, particularly the security and intelligence services,” Mr Barrett told Sky News on Thursday.

New recruits to Islamic State were reportedly required to fill out a 23-question enrolment form, which asked for such information as assumed name, birthplace, education level, work history and willingness to undertake a suicide mission. The responses to these forms were the subject of the leak.

The data was reportedly stolen by a twice-disillusioned militant who first fought against Assad, then with Islamic State, who then stole the data and leaked it.

The fighter reportedly became disaffected with IS because it had been taken over by former soldiers linked to Saddam Hussein. These men, members of Hussein’s Baath party, are likely to be less motivated by Islamic ideology and more by political and military strategy.

-with AAP