Any attempt by MPs to add a customs union to the government’s Brexit deal would be “procedural tricks” intended to frustrate departure, a senior minister has said, ahead of yet another potentially momentous day in parliament.

Rishi Sunak, the chief secretary to the Treasury, said the Speaker, John Bercow, should grant the government a second Commons vote on its deal on Monday, and that it would be “slightly odd” if he did not.

The expectation is that Bercow will not permit such a vote given that the deal was debated by MPs on Saturday, and a backbench amendment attached, putting off final approval until the legislation surrounding the plan is agreed.

Asked about the tight timetable surrounding departure from the EU – the government wants MPs to sit late or at the weekend if needed to meet the 31 October deadline – Sunak said parliament would have plenty of time to scrutinise the plan.

He also said economic impact assessments of the deal were not necessary as MPs should first approve the process of withdrawal, and then focus on the future relationship with the EU.

Labour is expected to seek to amend Brexit legislation to attach a UK-wide customs union, something it hopes the DUP, which opposes the plan negotiated by Boris Johnson, could back.

Sunak said amendments such as a customs union or making support for the deal conditional on a confirmatory referendum, were meant to wreck the process.

“People who are wanting to amend legislation are ultimately wanting to frustrate, delay or cancel Brexit altogether, and we should be clear about that,” he told BBC Radio 4’s Today programme.

“We have a deal that has been negotiated with the EU, that they themselves are happy with, and now want to get on with. I think everyone will look at that and think, this isn’t the time for more games in parliament, more amendments, more procedural tricks, which are just covers for trying to frustrate Brexit altogether.”

Speaking earlier to BBC1’s Breakfast programme, Sunak said economic assessments were not needed: “What we’re talking about when we talk about economic assessments is the future relationship, and that obviously is something that needs to be negotiated. Parliament will have its say on that process.

“But I would say this: this is about restoring trust in politics, ending the division of the last three years. No impact assessment or spreadsheet could convey the value of doing that if we could support this deal.”

Sunak said he would expect Bercow to grant a second vote: “The Speaker has always said that he would allow parliament to find a way to express an opinion on something. I think it’s pretty clear that parliament does want to express an opinion on this incredibly important matter.”

But Jonathan Ashworth, Labour’s shadow health secretary, said he would be surprised if Bercow allowed a fresh vote.

“The government is trying to bring back a vote that was dealt with in the House of Commons on Saturday,” he told Today. “I don’t understand how that is within the rules of the House of Commons, given on Saturday we amended that motion and that motion passed.”

Ashworth, who said it was “utterly irresponsible” that MPs should be asked to approve a Brexit plan without even seeing the associated legislation, rejected the idea that a customs union amendment was an attempt to derail the process.

“We’re not attempting to wreck it,” he said. “We’re attempting to safeguard the British economy, to safeguard jobs and public services.”

Johnson was forced to send the EU a letter seeking another Brexit extension after his first attempt to push his deal through the Commons on Saturday was amended, although the EU will wait to see whether this will be needed.

Ministers are hopeful that if Bercow was to allow another vote, Johnson might have a sufficiently large coalition of MPs for it to pass, with the help of some Labour rebels and the bulk of the strongly pro-Brexit wing of the Conservative party.

Steve Baker, who chairs the Tory hardline Brexit supporting European Research Group, said he was committed to the deal – and said the DUP should do the same, despite the party’s opposition to separate customs arrangements for Northern Ireland under Johnson’s plan, something the PM had previously ruled out.

“The point is that for people like me, vast areas of that withdrawal agreement are unchanged, and we are going to have to choke down our pride and vote in the national interests to get Brexit done, and that’s what we’re going to be doing.”

“I am afraid I am asking the DUP, just as we are having to choke down extremely difficult compromises to get out in the national interest, I think on this issue,” he told Today.

“This is a potentially a temporary arrangement, which will be superseded with a free trade agreement. I would ask the DUP to accept this compromise.”