A former member of both the Provisional IRA and the INLA has submitted a statement to the Bloody Sunday inquiry in which he accuses Mr Martin McGuinness of Sinn Féin of using the cover of the Bloody Sunday march to plan a nail-bomb attack in the city centre.
He also claims Mr McGuinness helped arm the eight nail-bombers chosen to carry out the attack with 16 bombs.
The 37-page statement of Mr Paddy Ward was submitted to the inquiry last month. It contains a series of highly controversial allegations against Mr McGuinness who, on Bloody Sunday in January 1972, was second in command of the Provisional IRA locally.
Fifteen years ago Mr Ward was suspected of being an INLA informer. He was abducted and taken across the Border from Derry into Co Donegal, where it is believed he was beaten and tortured by Dominic McGlinchey, the leader of the INLA.
Mr Ward managed to escape, and it is believed he fled to Canada. In February 1994 McGlinchey died in a gun attack near his home in Drogheda. That murder is believed to have been carried out by his former INLA associates.
Mr Ward claims Mr McGuinness played a central role in a bombing operation which was called off at the last minute because the security forces prevented the civil rights marchers from entering the city centre on the day.
He alleges Mr McGuinness arranged for the supply of 16 detonators for the nail-bombs just hours before the march and that he was at an IRA meeting where they were distributed. He claims two of the nail-bombs were given to Gerry Donaghy, on whose body four nail-bombs were found after he was shot dead on Bloody Sunday. Twelve other civilians were also shot dead by paratroopers on that day.
Because of the nature of Mr Ward's allegations, Mr McGuinness held a meeting with his legal adviser in Derry on Tuesday and is preparing to make a fresh statement to the inquiry rebutting the allegations. His legal adviser described the allegations as "ridiculous" and added: "Mr McGuinness will defend himself against these ridiculous accusations when Mr Ward presents himself at the inquiry."
It is understood Mr Ward will give his evidence in London next month.
He says in his statement that at the time of Bloody Sunday he was in the Derry Fianna, the junior wing of the Provisional IRA, and he claims he was recruited into the group by Mr McGuinness.
Four days before the planned civil rights march he attended a meeting of IRA members at which Mr McGuinness said the march "was an opportunity to get into Guildhall Square" to carry out a nail-bomb attack on commercial premises. Gerry Donaghy was also at the meeting. Mr Ward says Mr McGuinness asked what explosives they had and was told they had 30lb of explosives, gelignite, together with tape and nails.
Mr Ward claims Mr McGuinness ordered that the nail-bomb attack take place only after the crowd had dispersed from Guildhall Square and that the bombers were to mingle with the marchers to get into and out of the area. He says that on the Friday before the march, he again met Mr McGuinness.
"I asked about detonators which would be needed and I was told by Martin McGuinness that they would be supplied," his statement says.
On the eve of the march, Mr Ward says, he and five other Fianna members made the 16 nail-bombs.
"I had arranged with Martin McGuinness to meet him around midday on Sunday and pick up the detonators at the garages behind the Bogside Inn, so on Saturday night all was ready except for the detonators."
Mr Ward says that just hours before the march, Mr McGuinness and Colm Keenan, who was the IRA's explosives officer, "provided us with the detonators for the nail bombs we had previously made". Keenan was shot dead by British soldiers in Derry six weeks later. His statement continues: "Each man was then issued with two nail-bombs. I can confirm that Gerard Donaghy was given two nail-bombs, the same as everybody else."
When the bombing was aborted after the march was diverted, he says he ordered the bombers to return the devices to a prearranged arms dump.
"Of the 16 nail-bombs issued, 14 therefore came back. I do not know what happened to the two nail-bombs issued to Gerry Donaghy, but they were not the nail-bombs found later in the day."
However, he says that the four nail-bombs later found on 17-year-old Donaghy's body when the car taking him to hospital was stopped by soldiers were "not the type of nail-bomb that Gerard Donaghy had with him".
Mr Ward says it was suggested he had "something of a vendetta against Martin McGuinness and family because there has been bad blood between us in the past.
"While there have certainly been incidents between Martin McGuinness and me, my motivation in talking to the Bloody Sunday inquiry is solely to tell the truth about Bloody Sunday".