A former Ulster Unionist junior minister at Stormont has become the third member in recent months to defect to the Conservatives.
James Leslie has moved to the Conservative Party
James Leslie said NI politics had grown stale and the landscape was evolving.
Ulster Unionist leader Sir Reg Empey said he understood and shared Mr Leslie's frustration.
Mr Leslie won an Assembly seat in 1998, briefly becoming a junior minister in 2002, although he didn't stand in the Assembly elections of 2003.
In June, Peter Bowles and Philip Smith both announced their decision to move from the UUP to the Conservative Party.
Mr Leslie said the main reason for his decision to leave was his strong support for Conservative values.
"To get serious policy development you need the resources of a national party.
"You can see that clearly in all the political parties in Northern Ireland, there is no serious or fresh thinking."
Ulster Unionist leader Sir Reg Empey said he understood Mr Leslie's concerns.
"I want to be able to deal with those things, but we can't really concentrate on them until we get this matter resolved as to whether we are going to have devolution or not," he said.
"I hope that in the next couple of months, bringing that to a head is the right thing to do."
It is another blow for Sir Reg Empey's party, though arguably not as serious as the loss to the Tories in June of party officer Mr Bowles who was seen as a potential rising star.
Welcoming Mr Leslie's move, the Conservatives' Northern Ireland spokesman David Lidington said it was an indication that more and more people were recognising that the party was serious about organising in Northern Ireland.
Although membership is said to be growing, the local Conservatives cannot say how many members they have in Northern Ireland.