David Trimble, the former UUP leader, has said the Orange Order is in a dire state compared to a decade ago and was being politically manipulated.
He accused his opponents of "a Faustian pact" and using the order as "a battering ram" that they would use to destroy the Belfast Agreement".
He was speaking in Belfast at the launch of The Orange Order: A Tradition Betrayed by Brian Kennaway. The publication of the book, and Mr Trimble's criticisms, coincide with confirmation that the order has been in talks with Irish Government officials. It is also to hold talks with the SDLP next week while senior order members, acting in a personal capacity, are to have talks with nationalist residents' groups in Belfast.
Mr Kennaway, a Presbyterian minister from Co Antrim, says the book is part of a mission to force the order to see itself as it really is. "It is written with the wider community in mind, not just the Orange Order itself or even the Protestant-unionist community, to inform them, to explain North and South the historical background and the present dilemma of the Orange institution.
"That dilemma as I see it is this - is the Orange institution a political organisation with a religious element, or is it a religious organisation with a political element?"
Referring to the Republic, Mr Kennaway added: "The Orange Order can go forward if it realises that the Ireland dominated by 'Popery' has gone. Therefore there is no need for the anti-Catholic rhetoric. The institution has an image problem, but you cannot change the image without changing the practice, and the current leadership appears unable or unwilling to do that."
Mr Trimble said of the author that "he tells the simple truth" about the order, and a truth that in its detail made for "rather uncomfortable reading".
He said the order had been manipulated "with the intention of creating massive public disorder and violence, so that it would have a political impact".
The Orange Order last night questioned the accuracy of the book's allegations. "Far from betraying the tradition of Orangeism, we have ensured that it has survived and prospered," it said.