Tens of thousands of documents containing the names, addresses, phone numbers and family contacts of jihadis who joined the Islamic State group have been given to Sky News, the broadcaster said Wednesday.

Sky reported that a disillusioned former member had handed over the documents on a memory stick that had been stolen from the head of the group's internal security police.

The documents are forms that IS recruits had to fill out in order to be accepted into the organisation, and contain information on nationals from 51 countries, the broadcaster reported.

"Sky News has informed the authorities about the haul," the news channel wrote on its website. No comment was immediately available from Britain's interior or foreign ministries.

Some of the documents reportedly contain the information of previously unknown jihadis located across northern Europe, the United States and Canada, as well as in North Africa and the Middle East, it said.

Richard Barrett, former global terrorism operations director at MI6, wrote on Twitter that the records would shed an "invaluable light" on who had joined IS.

"This is going to be an invaluable resource for analysts," he added.

Copies of the documents broadcast by Sky News showed that recruits would have to answer 23 questions including on their blood type, mother's maiden name, "level of sharia understanding" and previous experience.

Some of the names in the documents are of fighters who have been already identified, such as Abdel-Majed Abdel Bary, a former rapper from west London who once posted an image of himself on Twitter holding a severed head.

Another named is Junaid Hussain, a cyber-operative for IS from the British city of Birmingham who was killed in a drone strike last August, and 21-year-old Reyaad Khan who appeared in a recruitment video and was killed last year.

The documents were obtained from a man who uses the name Abu Hamed, a former Free Syrian Army member who joined IS.

He stole the memory stick of documents and handed them over in Turkey to a journalist, explaining that he left because Islamic rules had collapsed inside the group.

Hamed claimed the group had given up on its headquarters in the Syrian city of Raqqa and was moving into the desert.