Parliament should hold an inquiry into how widespread collusion between loyalist paramilitaries and security forces in Northern Ireland was allowed to take place, Mr David Trimble said today.
The Ulster Unionist leader rejected calls for a full judicial investigation following publication of Sir John Stevens' report yesterday.
But he said the all-party Parliamentary Intelligence Committee, which sits in private, could examine what happened.
The SDLP and the widow of Pat Finucane, the Catholic solicitor murdered as a result of the collusion, have called for a full inquiry to see how high up the chain of command it went.
"The last thing we want is another full judicial inquiry when we see what is happening in terms of the time and money that has been expended elsewhere," Mr Trimble told the BBC Radio 4 Today programme.
"Yes there has been investigation, a lot of that investigation necessarily has been kept as it were private. There are still paramilitary organisations in existence, there are still people informants in that.
"Are the SDLP suggesting that we should now bring all that into the open? "Particularly when these organisations are still active and there is still a need to penetrate them in order to restrain their continuing illegal activities."
The Parliamentary Intelligence Committee should carry out an inquiry, Mr Trimble said.
"I think one should now look towards that intelligence committee, which is an all-party committee in Parliament.
"If there are any further inquiries, any further matters to be looked at, that is the best way to proceed."
It emerged yesterday that elements within Special Branch and military intelligence attempted to block Metropolitan Commissioner Sir John's investigation of the collusion, which left several innocent Catholics dead, including Mr Finucane.
PA