Party veteran Ken Maginnis quit the Ulster Unionists yesterday after challenging new leader Mike Nesbitt to stand down in a blazing row over gay marriage.
He resigned disillusioned and disenchanted with a party he served for 50 years claiming: "There is no room for independent or logical thinking and that does not suit me."
The former Fermanagh and South Tyrone MP fell out with Mr Nesbitt three months after he endorsed the ex-UTV presenter's leadership of a party which once dominated politics in Northern Ireland but which is now in deep electoral trouble without a representative at Westminster.
Lord Maginnis, from Dungannon, Co Tyrone, announced his resignation after the UUP leadership distanced themselves from him when he described gay marriage as "unnatural and deviant behaviour".
Lord Maginnis also described gay relationships as a “rung on the ladder” towards bestiality.
The 74-year-old peer, married with four children, later insisted he stood by his remarks on gay marriage, referring to "unnatural physical acts" by "deviants".
He added: "These are people that seem to take some pride expressing their particular rights. I disagree with those rights and that deviance."
Mr Nesbitt and senior party members were clearly embarrassed by his attack and this ultimately led to his resignation.
The peer was suspended from the party whip in June in response to his gay marriage comments, but the UUP leader offered to restore the whip yesterday in a bid to stop him from resigning.
Mr Nesbitt made the offer just hours before the resignation in an effort to heal the rift with one of the party's most senior and influential members. But he turned it down.
Lord Maginnis said: "If ever there was a hollow gesture in the 11th hour, that was it."
Mr Nesbitt said: "This is not the outcome I have been seeking -- quite the opposite, in fact. On behalf of the party and the unionist people more widely, we owe a debt of gratitude to Ken Maginnis.
"He was a fearless advocate of the Unionist cause, serving the community as a teacher, an officer in the Ulster Defence Regiment as well as a public representative during his time in elected politics."
Lord Maginnis was an MP from 1983 to 2001. He served in the controversial B-Specials and was later a major in the UDR.
Before he entered politics full-time he was a teacher, rising to principal of Pomeroy Primary in 1966.