Theresa May has refused to guarantee MPs will get a vote on the final Brexit deal to be thrashed out with the 27 EU leaders.
The Prime Minister was repeatedly asked whether the deal would be put to Parliament, as it will to the European Parliament, in her "end of term" appearance in front of the Liaison Committee.
The furthest Mrs May would go was to say that Parliament would have "ample opportunity to comment on and discuss the aspects of the arrangements that we are putting in place".
:: AS IT HAPPENED: MPs may not get vote on Brexit plan
When pushed by the chairman of the committee, Andrew Tyrie, to answer yes or no on a final deal vote for MPs, the Prime Minister simply said: "The answer I gave is the answer I gave".
She added: "There seems to be this idea that somehow we are not letting Parliament do anything.
"We have made statements to Parliament, we are having debates in Parliament, there will be the Great Repeal Bill, there is a whole variety of commitments we have given to Parliament.
"We will make sure that Parliament has the opportunity to discuss these matters as we go through thenegotiations."
:: Bad Brexit deal could trigger new Scotland referendum
Brexit select committee chairman Hilary Benn also came up against a brick wall and later tweeted: "Why can't the PM commit to MPs voting on the final Brexit deal when David Davis has said that it would be 'inconceivable' for them not to?"
The committee hearing came against a backdrop of increasing frustration from MPs over the Prime Minister's refusal to give "a running commentary" on Brexit.
Mrs May said she would be making a speech "early in the new year" setting out further Brexit details.
She said she would publish a Brexit plan before MPs voted on triggering Article 50 at the end of March, but would not give a date on when those proposals would be released.
During the question session, there were testy scenes with the chair of the Home Affairs Select Committee, Labour's Yvette Cooper, over migration figures and how Mrs May would tackle them.
Ms Cooper asked the Prime Minister how she would reach her net migration target of "tens of thousands" and asked if she would be putting forward immigration measures with the Brexit plan.
She said Mrs May would need to cut EU net migration from 189,000 to around 50,000 and asked her if she would be prepared to stick to her targets even if it was at the expense of British interests in terms of business.
The Prime Minister said she was not expected to extend the Article 50 negotiating period beyond two years.
However, she admitted that if the European Parliament voted against the final deal then EU leaders would have to ask to extend the deadline - if they wanted negotiations to continue.
But she dismissed claims by the UK ambassador to the EU, Sir Ivan Rogers, that it could take 10 years to reach a trade deal.
The Prime Minister said Government departments were preparing for the "worse case scenario" of the UK leaving the EU with no deal.
She said: "We are looking at a variety of scenarios that could come forward in relation to the negotiation, the deal, the timing and what other opportunities would be there."
Mrs May also said there would likely be an "implementation period" after Brexit to give businesses a chance to adapt but she stressed this would not be a delay of Brexit.