One of the leading Conservative architects behind plans to stop no deal has said MPs do have time to pass legislation on it, but denied plans were being coordinated with the House of Commons Speaker.

However, MPs from different parties are believed to be still at odds over the details of what any legislation to halt no deal should be, how to stop Boris Johnson from circumventing any new law, and crucially what the aim of any extension to article 50 should be, whether extra time for negotiations, a second referendum or a general election.

Sir Oliver Letwin, who led efforts to stop no deal earlier this year by passing a bill with the Labour MP Yvette Cooper, said “there probably is time” to get a measure to block a no-deal Brexit through parliament.

A number of prominent Conservatives, including the former cabinet ministers Philip Hammond, David Gauke and Rory Stewart, have indicated they will back the efforts next week but Letwin said he was not complacent about numbers.

“It’s a foolhardy person who predicts the number of MPs who will vote either way on an issue of this kind and we will just have to see whether we can acquire a majority of the required kind,” he said on Friday.

“I know that there are a number of my colleagues who feel as I do, that a disorderly no-deal exit is a very bad idea, and they have in the past been willing to come and support efforts to prevent that happening and I very much hope that will happen again.”

A senior MP close to the rebels’ discussions said all efforts would be on passing a bill forcing the government to request an extension, but there were still question marks over how long an extension should be and for what purpose.

“Labour and the frontbench want a general election, soft-Brexit Tories like Letwin don’t want either a people’s vote or a general election and a significant number of the PLP [parliamentary Labour party] won’t vote for a referendum either,” the MP said.

“If the legislation is vague, as it was in the Cooper bill in April – where the extension length was unspecified – Boris could simply ask for another six hours’ extension and satisfy the legal requirement.”

Letwin denied reports that the House of Commons Speaker, John Bercow, had broken off his family holiday to discuss “cooking up plans” with him to stop parliament being prorogued.

“There’s no question of any MP cooking up any deal with the Speaker. You cannot do that. The Speaker has to follow the rules,” he told BBC Radio 4 Today programme.

“It’s perfectly true that over many months I have been speaking to the clerks and the Speaker to establish what the procedures are. I have talked to the Speaker and the clerks on many occasions and will continue to do so.”

Letwin said his focus would be on stopping no deal, rather than challenging prorogation of parliament. “It’s not my business to stop the prorogation. That is going on through the courts,” he said. “There are several court actions under way. I would like to see the prorogation not happen. Whether it is lawful or not, the courts will decide. That is not for MPs to decide.”

Shami Chakrabarti, the shadow attorney general, said she believed “this abusive early shutdown of parliament has strengthened those potential numbers” prepared to back action against no deal.

“You can never be absolutely certain until the moment you expect people to put up,” she told Today. “My own soundings and those of colleagues over the last couple of days since the constitutional outrage give me greater comfort that minds are now focused, particularly on the Conservative side.”

She added she was confident of any new law being passed through the House of Lords, and said MPs opposed to a no-deal Brexit would sit in parliament over the weekend if necessary. “I believe there are means of preventing any sort of public school dirty tricks working even in the House of Lords,” she said.

Opposition peers expect Tories in the Lords to attempt to filibuster the legislation, which will need to have passed through all its parliamentary stages and received royal assent before parliament is suspended or it will fall.

The Liberal Democrats’ leader in the Lords, Dick Newby, said the government could be defeated. “The government’s tactic to stop the bill in the Lords could be to pack it with hostile amendments and then attempt to filibuster the bill.

“On our side we can interrupt and put the amendments to a vote and, depending on how many there are, we could even sit all night every day through Thursday, Friday, Saturday and Sunday. We have the troops and we have the camp beds. People will be queuing up to stay.”