The North's power-sharing executive is unlikely to meet again, Mr David Trimble told the North's Assembly yesterday.
Asked during Ministerial Questions when the executive would next meet, he told the Assembly:
"I must say without dramatic developments, I have great difficulty in seeing how the executive, as presently constituted, can meet again."
Mr Trimble called on Ulster Secretary, Dr John Reid to conduct an inquiry into how republicans allegedly managed to infiltrate the highest echelons of government.
His party colleague David McClarty asked if it was conceivable that there would have been the same level of infiltration had the executive been responsible for security matters.
"Would the question of concealing the scale of stolen documents for over three months have arisen?" he added.
Mr Trimble told the Assembly: "There is no doubt of the fact that there are very serious questions that should be asked about how the Northern Ireland Office conducted its business and the level of regulation that existed there.
"I hope very much that in an appropriate time and not too far distant that the Secretary of State will institute a proper inquiry into what happened on his watch and put the matters in the public domain."
Mr Trimble would have to focus on the "counter-productive" actions of republicans rather than lashing out at party colleagues, one his chief critics in his own party said yesterday.
In a sign of continuing tensions within the UUP, Lagan Valley MP, Jeffrey Donaldson insisted he would not be silenced by his party leader despite claims by Mr Trimble that his comments on the current political crisis had not helped matters.
Responding earlier to weekend claims by Mr Donaldson that the power sharing executive with Sinn Féin would collapse within days, the Stormont First Minister said: "There are a number of possibilities in this situation and people know what they are in terms of exclusions, suspension.
"Whatever the options are, we will be asking the government and other parties to think hard and carefully about what they do and, in fact, we might be asking other parties to stretch themselves.
"The likelihood of them stretching themselves is diminished if the impression is given that the demand is being made on behalf of people who want to put an end to these institutions and to destroy the agreement and in that sense I have to say that I find some of Jeffrey's comments counter-productive. "
"I think the best thing Jeffrey could do is to reflect on the advice (prime minister Clement) Atlee gave to Harold Laski one time that 'a period of silence from you would be welcome'." But Mr Donaldson later said he stood by his comments.
"I think we have to keep focussed on the people who have been counterproductive in this process and that is the Republican Movement," the MP said.
"I have to say I would find it incredible if a party leader was to try and silence any of his MPs on speaking out on what is the most critical crisis to affect the process in many years.
"I know I am speaking for a majority of unionists who have deep concerns about these issues and I will continue to do so."
"I think we should all avoid getting into a personality debate and instead concentrate on the abuse of the democratic process by Sinn Féin/IRA."