Corbyn was investigated over fears he could've been a threat to national security
The story comes from the The Daily Telegraph, who said that the Labour party leader was investigated over fears he could have been a threat to national security.
The investigation was supposedly launched at a time when Mr Corbyn was campaigning for a unified Ireland.
According to the paper, he supported one of the Balcombe Street gang, which waged a 14-month bombing campaign, and also had links to a bombmaker believed to have been behind the Hyde Park and Regents Park attacks.
Responding to the Telegraph's claims, a spokesman for Mr Corbyn said: "MI5 kept files on many peace and Labour movement campaigners at the time, including anti-Apartheid activists and trade unionists.
"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.
He finished by saying "Jeremy campaigned for fair trials and against miscarriages of justice, after a series of well-publicised cases, such as the Guildford Four and the Birmingham Six."
The source involved with the story told the Telegraph: "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."
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", the source added.
The Metropolitan Police's Special Branch was also monitoring Corbyn around the same time, but it is unclear if the intelligence was shared.
The paper says Peter Francis, an undercover officer turned whistleblower, revealed that the force secretly compiled files on Mr Corbyn and nine other MPs which detailed their political beliefs, personal background and any demonstrations that they attended.
It is also claimed that the London Labour Briefing, a magazine which Mr Corbyn sat on the board of and frequently contributed to was being monitored by the security services.
At the height of the Troubles, Mr Corbyn was a regular face at Republican protest events.
On one occasion it was reported in a Sinn Fein newspaper that he shared a platform with an IRA volunteer who was wanted over the killing of an SAS soldier.
The Telegraph reports that Mr Corbyn was also visited in the House of Commons by Gerard McLochlainn, the former "voice of Sinn Fein in London", who had recently been released from prison for conspiracy to detonate explosives, and Linda Quigley, who had also been recently released from a sentence for IRA-related offences.