Speaker John Bercow has vowed to use “procedural creativity” against the Prime Minister if he attempts to break the law over Brexit.
Boris Johnson is currently bound by new legislation to request an extension to the Brexit deadline if Parliament does not approve any deal - or a no deal exit - by October 19.
However, Mr Johnson has said he would rather be "dead in a ditch" than ask for a delay until January 31.
But the outgoing Commons Speaker, who announced his upcoming resignation this week, said if Mr Johnson were to come close to breaking the law, Parliament "would want to cut off such a possibility and do so forcefully".
"If that demands additional procedural creativity in order to come to pass, it is a racing certainty that this will happen, and that neither the limitations of the existing rule book nor the ticking of the clock will stop it doing so," Mr Bercow added.
The outgoing Speaker's warning came as the EU's chief negotiator said there is "no reason to be optimistic" that a new agreement can be reached before the Prime Minister's deadline to ask for a delay.
Michel Barnier told political leaders in the European Parliament that he was unable to say whether contacts with the UK Government would result in a deal by mid-October.
"We will see in the coming weeks if the British are able to make concrete proposals in writing that are legally operational," he said.