Ian Paisley, Northern Ireland's first minister, who has dominated Ulster unionism since his rabble-rousing appearances at the start of the Troubles in the 1960s, is to bow out of politics within months, according to senior sources on both sides of the Irish sea. A gentle campaign to ease out the man who made his name as "Dr No" is intensifying at the highest levels of the Democratic Unionist party after the resignation of Paisley's son, Ian Jr, as a minister in the Northern Ireland assembly over allegations that he lobbied Downing Street on behalf of a wealthy party member. London and Dublin expect that Paisley could stand down as first minister as early as May - just a year after he found himself dubbed "Dr Yes" for the first time when he entered into a power sharing executive with Sinn Féin. "It is now expected that Ian Paisley will be gone by May," a senior government source said. Paisley, who will be 82 in April, refused to comment on his future yesterday when he embarked on an official tour of Scotland with his son and his deputy in the power-sharing executive, Sinn Féin's Martin McGuinness. "I've no comment whatsoever," he said in answer to questions about his future. But DUP sources confirmed that his days as party leader - and therefore as first minister - are numbered after the departure of his son. "There is no doubt the resignation of Ian Jr is a big blow to his father," a well-placed DUP figure said. "If you'd asked anyone six months ago about his position you would say that he would have served a full four-year term as first minister. But that has changed. He will now go sooner rather than later." Paisley's departure will draw to a close one of the most extraordinary political careers in the history of Northern Ireland. He was blamed by many for whipping up sectarian hatred in the 1960s when he responded to the campaign for civil rights by mounting counter-demonstrations, many of which turned violent. Gerry Adams, Sinn Féin's president and the dominant figure in republicanism since the 1970s, recalls how he was drawn into militant republicanism as a 16-year-old when he watched Paisley provoke a riot in 1964. Republicans and loyalists rioted for two days after the fiery 36-year-old Protestant preacher demanded that the police tear down an Irish tricolor from Sinn Féin's office on the Lower Falls Road. For the next three decades Paisley opposed every attempt at power sharing and cooperation with the Irish government. He played an instrumental role in the strikes which ended the first experiment in power sharing in 1974 and opposed the 1998 Good Friday agreement. As he entered his ninth decade, Paisley embarked on the monumental step of sharing power with Sinn Féin. He and McGuinness have worked so well that they have been dubbed the "Chuckle Brothers". Sinn Féin accepts that Paisley will be gone soon and that McGuinness will be working with a new first minister, likely to be Peter Robinson, the deputy leader of the DUP, who is Northern Ireland's finance minister. Robinson is understood to have received assurances from Paisley which have persuaded him not to precipitate his leader's downfall. "It is most unlikely that Ian Paisley will go before May because Peter Robinson does not want to mount a coup," a senior government source said. "He does not want to have Ian Paisley standing over his shoulder saying this is how I would have done things. But Paisley will probably be gone by May: to wait longer will make Robinson look weak."