Published Tuesday, 28 August 2012
Lord Maginnis said he left the party with considerable regret but said after 50 years in politics that he couldn't allow himself to be "gagged".
It follows a dispute with the party leader over comments he made about gay marriage.
On Tuesday Lord Maginnis claimed that, after Mr Nesbitt was elected, the new leader avoided seeing him.
"I would have expected as a senior member of the party, to be seen almost immediately and that's not self-flattery, that's the practicalities of running a party, a party that should have policies and a party that should be demonstrating direct concern for the welfare of our community," he told UTV.
Mr Maginnis accused the leader of using the gay marriage comments as an excuse to push him out of the party.
He added that he did not encourage his colleagues to follow in his footsteps.
But the peer said that, in his view it was a mistake to elect Mike Nesbitt as leader, but added it was "up to the party to decide".
In June Lord Maginnis spoke out in strong opposition against allowing same-sex couples to marry in church during a BBC radio debate, repeatedly referring to it as "unnatural and deviant behaviour" which shouldn't be "imposed" on society.
The senior politician said that gay relationships were "a rung on the ladder" towards bestiality.
At the time the Ulster Unionist Party distanced itself from his controversial remarks and stressed that he was speaking in a personal capacity and not for the party.
Mr Nesbitt later withdrew the party whip from Lord Maginnis.
Reacting to the announcement on Tuesday, Mr Nesbitt expressed his regret at Lord Maginnis's decision to resign.
"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 said in a statement.
"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.
"He was the sort of progressive unionist I admire. I regret we will not have access to his experience and expertise as we move to rebuild and revive this great Party. However, 50 years service is a lifetime's devotion, and I must respect his decision."
He added: "I hope we can now focus on a legacy of service over a number of decades rather than concentrate on more recent matters, which I believe could have been resolved at any time."
© UTV News