Labour-led attempt to stop the UK leaving without a deal is defeated, in move that could help Boris Johnson

Conservative leadership candidates including Boris Johnson hoping to force a “deal or no deal” Brexit in October have been handed a boost after MPs defeated a Labour-led attempt to tie the next prime minister’s hands.

Labour vowed it would not end efforts to stop no deal but the defeat bolstered Johnson’s claim at his leadership launch that MPs would not be prepared to “reap the whirlwind” of halting Brexit entirely as Tory MPs prepared for the first round on voting to choose the next prime minister on Thursday.

Tory MPs cheered as the motion was defeated by a majority of 11 on Wednesday night, after which Jeremy Corbyn was heard to say: “You won’t be cheering in September.”

The former Conservative MP Nick Boles warned opponents of a no-deal departure were fast running out of options – apart from a confidence vote to bring down the government. “No-deal Brexit on 31 October is back to being a racing certainty,” he said. “It is very hard to see where any further legislative opportunities will come from. So it’s now a question of politics – specifically whether a PM pursuing a no-deal Brexit can command and sustain the confidence of the House of Commons.”

Johnson officially launched his campaign on Wednesday saying he believed a new government “with a new mandate, a new optimism, a new determination” could leave the EU with an amended deal by 31 October.

However, the leadership frontrunner warned that he was determined to leave the EU by that date, whether he had achieved a new deal or not.

“I am not aiming for a no-deal outcome, I don’t think we can end up with any such thing. But it is only responsible to prepare vigorously and seriously,” he said.

Johnson refused to say what he would do if he had not secured an improved deal in time for 31 October – or whether he would resign if the deadline were not met or no deal was prevented.

Q&A What does a no-deal or WTO-rules Brexit mean? Show Hide If the UK leaves the EU without a deal it would by default, become a “third country”, with no overarching post-Brexit plan in place and no transition period. The UK would no longer be paying into the EU budget, nor would it hand over the £39bn divorce payment. The UK would drop out of countless arrangements, pacts and treaties, covering everything from tariffs to the movement of people, foodstuffs, other goods and data, to numerous specific deals on things such as aviation, and policing and security. Without an overall withdrawal agreement each element would need to be agreed. In the immediate aftermath, without a deal the UK would trade with the EU on the default terms of the World Trade Organization (WTO), including tariffs on agricultural goods. The UK government has already indicated that it will set low or no tariffs on goods coming into the country. This would lower the price of imports – making it harder for British manufacturers to compete with foreign goods. If the UK sets the tariffs to zero on goods coming in from the EU, under WTO “most favoured nation” rules it must also offer the same zero tariffs to other countries.

WTO rules only cover goods – they do not apply to financial services, a significant part of the UK’s economy. Trading under WTO rules will also require border checks, which could cause delays at ports, and a severe challenge to the peace process in Ireland without alternative arrangements in place to avoid a hard border.

Some no-deal supporters have claimed that the UK can use article XXIV of the General Agreement on Tariffs and Trade (Gatt) to force the EU to accept a period of up to 10 years where there are no tariffs while a free trade agreement is negotiated. However, the UK cannot invoke article XXIV unilaterally – the EU would have to agree to it. In previous cases where the article has been used, the two sides had a deal in place, and it has never been used to replicate something of the scale and complexity of the EU and the UK’s trading relationship. The director general of the WTO, Roberto Azevêdo, has told Prospect magazine that “in simple factual terms in this scenario, you could expect to see the application of tariffs between the UK and EU where currently there are none”. Until some agreements are in place, a no-deal scenario will place extra overheads on UK businesses – eg the current government advice is that all drivers, including lorries and commercial vehicles, will require extra documentation to be able to drive in Europeif there is no deal. Those arguing for a “managed” no deal envisage that a range of smaller, sector-by-sector, bilateral agreements could be quickly put into place as mutual self-interest between the UK and EU to avoid introducing or to rapidly remove this kind of bureaucracy. Martin Belam

Speaking after the defeat in the Commons, the shadow Brexit secretary, Keir Starmer, said Labour would continue its cross-party efforts to stop no deal.

“Labour stands ready to use whatever mechanism it can to protect jobs, the economy and communities from the disastrous consequences of a no-deal Brexit,” he said. “Any Tory leadership candidate should know that parliament will continue to fight against no deal.”

One shadow minister said opponents of a no-deal Brexit had missed a crucial opportunity and believed they had been scuppered by the timing. “This isn’t the end of it. We’ll just have to be doubly creative,” they said. “The timing in the midst of [the] Tory leadership [contest] is poor, but not our choice.”

Eight Labour MPs including Caroline Flint, John Mann and Graham Stringer voted with the government against the motion and 13 more abstained. Ten Conservative MPs voted with Labour.

The debate before the vote revealed fraying tempers in all wings of both parties. The Labour MP Gareth Snell, who represents the leave-voting seat of Stoke-on-Trent Central, said he regretted not voting for Theresa May’s Brexit agreement. He said he would abstain because he could not countenance parliamentary manoeuvres that would lead to a further delay.

“We will have been responsible for a no-deal Brexit by default because of our inability to make a decision,” Snell said.

The former attorney general Dominic Grieve said he was prepared to resign the Conservative whip and go against the government in a no-confidence vote if it would prevent a no-deal Brexit. “I simply have to say, here and now, I will not hesitate to do that if that is what is attempted,” he said.

The motion proposed giving MPs control of the parliamentary agenda in a fortnight’s time. That day could then have been used to begin legislation to prevent the UK from leaving the EU without a deal, though it is uncertain what form this would take.

Speaking in the debate, Starmer said MPs had been forced to act because of suggestions from leadership candidates including Johnson and Dominic Raab that the UK would leave – come what may – on 31 October. Raab had even suggested he would be prepared to prorogue parliament to stop MPs’ efforts to prevent a no-deal Brexit.

“It will introduce a safety valve in the Brexit process and it will be a reminder to all Conservative leadership candidates that this house will take every step necessary to prevent a no deal,” Starmer said.

The motion, which Labour tabled during an opposition day debate, was signed by the former Conservative minister Oliver Letwin and the leaders of the Scottish National party, Plaid Cymru, the Liberal Democrats and the Green party.

The Brexit secretary, Steve Barclay, said it was a “blind motion” that gave no indication as to what path MPs would try to pursue to block a no-deal departure, and would have “virtually unlimited scope”.

Tory MPs who said they intended to back the plan included Grieve, Antoinette Sandbach, Sam Gyimah and Jonathan Djanogly, plus Boles, who had flown back to the UK specifically to vote on the motion.

MPs working across parties believed it was essential to try to start efforts to halt a no-deal Brexit before the next prime minister was installed and prior to the start of the summer recess. There are no further opposition day debates scheduled.

Tory leadership candidates including Matt Hancock and Rory Stewart, who have opposed no deal, had earlier made it clear they would not back the motion.

But Hancock told the Guardian: “It’s no good just having a Brexit position that is built on either re-running the old plan, which failed; or threatening no deal, when parliament has voted in the past already to block no deal. No deal isn’t a policy choice that is available to the next prime minister.”

Earlier, Philip Hammond said Johnson’s Brexit plan was impossible as the UK will not be able to leave the EU with a deal or without a deal by the end of October.

Hammond cast doubt on the viability of the Brexit promises of Johnson and other Tory leadership contenders as he gave a speech in Westminster.

He said many of the candidates were pledging things that they could not deliver. Asked whether Johnson’s plan to leave on 31 October would work, he said: “I don’t think so … I think it’s not sensible for candidates to box themselves into a corner on this. Parliament will not allow a no-deal exit from the EU and our experience has suggested it may not be that easy to secure a deal in parliament.”

The idea of leaving with a deal by that date would be “very difficult or impossible”, he said.

Leadership contender Jeremy Hunt was also asked about Hammond’s comments and said: “This is a time for skilled negotiation and not empty threats. I’ve always wanted to keep no deal on the table as one of our negotiating levers but we can’t be blind to the fact that there is a strong majority in parliament against no deal and it’s likely that parliament would find a way to block no deal if that was being pursued by the prime minister.

“That’s why we need to find a way through this that gets us a deal. And if we want Brexit we need to choose a prime minister who can get us a deal.”