British intelligence, the MI5 opened a file on UK's main opposition leader Jeremy Corbyn amid concerns over his links to the Irish Republican Army (IRA), the media reported.
The Labour leader was probed over fears that he could have been a threat to national security at a time when he was supporting convicted terrorists and campaigning for a unified Ireland, The Telegraph reported late Friday.
The revelations come as a Telegraph investigation revealed Corbyn's full links to the IRA, including his support for one of the Balcombe Street gang, who waged a 14-month bombing campaign across south-east England, and his links to the bomb maker believed to have been behind the 1982 Hyde Park and Regents Park attacks.
It was against the background of his support for the IRA that caused the MI5 to begin looking into Corbyn's activities, and a source close to the investigation confirmed a file was opened on him by the early 1990s.
"If there was a file on someone, it meant they had come to notice. We opened a temporary file and did a preliminary investigation. It was then decided whether we should open a permanent file on them," the source told The Telegraph.
A file would be opened on "someone who sympathises with a certain group, or is friends with a specific person" and the purpose was to "assess whether the person was a threat", he added.
Peter Francis, an undercover officer turned whistle-blower, has revealed that the MI5 did secretly compile files on Corbyn and nine other MPs which detailed their political beliefs, personal background and any demonstrations that they attended.
Corbyn has been questioned over his links to the IRA and during his leadership campaign refused five times during a BBC interview.
A spokesman for Corbyn said on Friday night: "Jeremy campaigned for peace in Northern Ireland. To do so, he campaigned for the rights of all to be respected and spoke to people on all sides of the conflict."
"Jeremy campaigned for fair trials and against miscarriages of justice."