Boris Johnson has refused demands to categorically rule out suspending parliament to push through a no-deal Brexit without the consent of MPs.

The frontrunner to be the next prime minister confirmed it was one of the options on the table, after failing to give clear answers on several other occasions.

Johnson said on Wednesday that the chance of a no-deal Brexit was “a million to one against”, but he has also promised to completely replace the “defunct” withdrawal agreement negotiated by Theresa May and leave the EU by 31 October. The EU has repeatedly said the deal is not up for renegotiation, leading the odds of leaving without a deal to rise.

Speaking at a hustings for Conservative members in Bournemouth on Thursday, the former foreign secretary said he did not want to prorogue parliament to prevent MPs blocking a no-deal Brexit but it should not be removed as an option.

Profile Boris Johnson's Tory leadership campaign Show Hide Personal style A late-night altercation between Tory leadership favourite, Boris Johnson, and his partner, Carrie Symonds initially changed the dynamics of Johnson's campaign. He had been either invisible or deliberately sober to the point of dullness, when his usual primary draw to Tory members is a self-created sense of optimism and fun. Much is also made of his supposed broad appeal to the electorate, evidenced by two terms as London mayor. His bizarre claim to make model cardboard buses has raised eyebrows. In most political contests, Johnson’s character – he has lost more than one job for lying, and has a complex and opaque personal life – would be a big issue, but among the Tory faithful he seemingly receives a free pass. It remains to be seen what impact that late-night police visit will have on his chances. Brexit He has promised to push for a new deal while insisting the UK will leave the EU come what may on 31 October, even if it involves no deal. While his hard Brexit supporters are adamant this is a cast-iron guarantee of leaving on that date, elsewhere Johnson has been somewhat less definitive. Asked about the date in a BBC TV debate, Johnson said only that it was 'eminently feasible', although he then went on to tell TalkRadio that the 31 October deadline was 'do or die'. Taxation His main pledge has been to raise the threshold for the 40% higher tax rate from £50,000 to £80,000, at a cost of almost £10bn a year, which would help about 3 million higher earners, a demographic with a fairly sizeable crossover into Tory members. Johnson’s camp insist it would be part of a wider – and so far unknown – package of tax changes. Public spending He has said relatively little, beyond promising a fairly small increase in schools funding, as well as talking about the need to roll out fast broadband across the country. Johnson has generally hinted he would loosen the purse strings, but given his prior fondness for big-ticket projects – London’s cancelled garden bridge, the mooted 'Boris island' airport – perhaps expect more of a focus on infrastructure projects than services. Climate and environment This is unlikely to be a big issue for Conservative party members, and Johnson has not said much on this beyond confirming his general support for the new government target of cutting greenhouse gas emissions to a net zero by 2050. Foreign policy Also unlikely to be a big issue among Tory members, beyond vague platitudes on 'global Britain', it could be a weak spot for Johnson given his poor performance as foreign secretary. He was seen as something of a joke by diplomats – both UK and foreign – and is likely to face more questioning over his gaffe about the jailed British-Iranian woman Nazanin Zaghari-Ratcliffe Peter Walker Political correspondent Photograph: Isabel Infantes/AFP

Asked whether he would do it, he said: “I would rather than confiding in this archaic device to get this thing done at my own behest, I would rather confide in the maturity of common sense of parliamentarians, all of whom are now staring down the barrel of public distrust.”

He was then pressed to categorically rule it out and failed to do so, saying: “I’m not attracted to the idea of a no-deal exit from the EU but, you know, I think it would be absolutely folly to rule it out. I think it’s an essential tool of our negotiation.

I’m not attracted to the idea of a no-deal exit but I think it would be absolutely folly to rule it out Boris Johnson

“I don’t envisage the circumstances in which it will be necessary to prorogue parliament, nor am I attracted to that expedient.”

Johnson got the loudest applause of the hustings by saying he would take a different approach to the negotiations than May had done. He claimed to be an “irenic person” and in favour of dialogue but argued that “a little bit more resolve is called for and a little bit more sense that we can actually get this done”.

On domestic policy, he argued for students to be taken out of the immigration cap, reform of the student loan system to solve the social care crisis, and an extra £5bn to the school system.

He also criticised his rival, Jeremy Hunt, for pledging to cancel student debt for some entrepreneurs employing at least 10 people full time for five years.

“I think people, a lot of people, would automatically be defining themselves as entrepreneurs,” Johnson said.

Hunt opened his appearance at the hustings by saying the party should not pick a “populist” to fight Labour leader Jeremy Corbyn but “choose our own Jeremy” to stick up for business, aspiration and social justice for young people.

The foreign secretary also made a surprising pledge to resign as prime minister if he doesn’t manage to “deliver Brexit and deliver it very quickly”.

Asked by moderator Hannah Vaughan Jones if he was “concerned by threats it could be the shortest tenure in history”, he replied: “Well, if we get this wrong, it will be.

“And we have got the biggest constitutional crisis in living memory and that is because MPs like me made a promise to the people that we would deliver the outcome of the referendum whatever it was and we failed.”

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

He was then asked if he would resign if he failed to deliver the referendum’s result. “Of course, no prime minister is going to last any time at all if they don’t deliver Brexit and deliver it very quickly,” he replied.

“That’s the reality of British politics … That’s about anyone who does that job.”

As he sought to win over the highly Eurosceptic membership, he said he would introduce a “no-deal bill” in the first Queen’s speech in the new parliamentary session. He also said he would introduce new legislation to ensure every child leaves school able to read and write and got booed by the audience for committing to the HS2 highspeed rail line.

Profile Jeremy Hunt's Tory leadership campaign Show Hide Personal style His style is notably technocratic, with few rhetorical flourishes and an emphasis on his consensual approach and long record as a minister, notably during more than five years as health secretary, a traditional graveyard of ministerial careers. Hunt’s attempts to talk up a backstory as an 'underestimated' entrepreneur can fall flat given he is also the son of an admiral and was head boy at Charterhouse. Overall, Hunt’s approach can seem uninspiring and hard to pin down in terms of core beliefs, hence the 'Theresa in trousers' nickname among some Tory MPs. Hunt has made headlines by promising to repeal the ban on fox hunting, while always facing scrutiny on his views on the availability of abortion. His campaign team have decided to take the fight directly to rival Boris Johnson though, with Hunt taking part in a Twitter Q&A session as a direct response to Johnson's refusal to appear on a Sky TV head-to-head debate. The hashtag: #BoJoNoShow. Brexit He says a new deal with the EU is possible by 31 October and he would send a cross-party negotiating team to Brussels, including members of the DUP. He would countenance leaving the EU without a deal but is notably more wary than rival Boris Johnson. Taxation Has been fairly silent on this, beyond a proposal to cut corporation tax from 19% to 12.5%, which according to the IFS would cost an estimated £13bn a year. Even at 19%, the UK rate is well below European and global averages. Public spending Before the campaign began he called for a doubling of defence spending, but he has since pulled back slightly, saying only that it should increase. He has argued that cuts to social care budgets had gone too far. Climate and environment Hunt backs the 2050 target for zero net carbon emissions and has called for 'sensible tax incentives' to encourage green initiatives, but very little beyond this. Foreign policy A likely strength for him, as he has been seen as a solid foreign secretary, an impression burnished by taking over from the chaotic Johnson. This has been a key part of his pitch. Peter Walker Political correspondent Photograph: Luke Dray/Getty Images Europe

He was pressed about how he would fulfil his pledges without raising debt, after the Institute for Fiscal Studies said his tax and spending proposals amounting to more than £60bn could exacerbate pressures on public finances.

“All my commitments are funded through a pledge that I will keep reducing debt as a proportion of GDP over the economic cycle so we won’t be building up debt for future generations,” he said.

“We actually have now about £26bn of headroom a year, which is why we can afford some of these commitments.”