Kevin McQuillan, a former leading figure in the political wing of the Irish National Liberation Army, made the allegations at the Old Bailey.
Mr McQuillan, 34, from Belfast, is a defence witness in the trial of Martin McMonagle, 31, of Limerick, and Liam Heffernan, 31, of Belfast, who deny conspiracy to steal explosives, conspiracy to cause explosions and possessing a firearm with intent to endanger life.
The prosecution has alleged they were part of a three-man INLA team trying to steal explosives from a West Country quarry to mount a bombing campaign.
Both men were arrested after the informer, Patrick Daly, tipped off police.
Asked by Rock Tansey QC, for Mr McMonagle, about Mr Daly's attitude, Mr McQuillan said: 'He came across as a person who espoused the maximum use of violence as a means of achieving political ends . . . he accused people talking about the political situation of being soft, told them to get off the fence and involve themselves in acts such as armed action against the British state in Northern Ireland.'
The case was adjourned until today.