Former DUP mayor of Derry Maurice Devenney has claimed the party has moved away from the democratic principles espoused by its late founder Ian Paisley.
Mr Devenney formally resigned a week after he was suspended following claims he brought the DUP into disrepute. The party alleged Mr Devenney canvassed outside a polling station for SDLP MP Mark Durkan during last year's general election.
A veteran councillor, Mr Devenney replaced Stormont speaker Lord Hay when he stood down from the assembly. However, five months later Mr Devenney resigned the seat, stating he wished to focus on council issues.
A native of Co Donegal, Mr Devenney now intends holding his council seat as an independent unionist.
In a statement confirming his resignation, Mr Devenney alleged a campaign had been waged against him.
He said: "I refute totally that I was promoting the SDLP in preference to my own party at that time, the DUP."
He added that he decided to resign after "some time in deep and prayerful consideration".
"It is clear to me and my advisers that the party has moved away from the democratic principles espoused by the late Dr Ian Paisley," he said.
Mr Devenney said it was made clear to him that he would be selected by his local constituency association to contest the assembly elections but that the party hierarchy would not accept this. He said another candidate would be put forward.
A DUP spokesman said Mr Devenney's decision to leave the assembly was his own. He said this led many members to the belief that he would not have been a suitable candidate.
