Leading Brexiters have pushed back at claims that their campaign to “chuck Chequers” is going off the rails as they endorsed an alternative proposal that would result in the UK crashing out of the European Union without a deal.

Jacob Rees-Mogg, the chair of the pro-Brexit European Research Group, said there was “nothing to fear” from a no-deal scenario after the pro-Brexit economist Patrick Minford claimed it could boost Treasury revenues by £80m a year.

Mogg said, however, that he would prefer the government to strike a Canada plus-style free-trade deal with Brussels to retain the benefits of leaving on “the most friendly terms we can manage”.

The former Tory leader Iain Duncan Smith also said the government could move on to World Trade Organization rules or opt for a “proper, substantial” free-trade deal with the EU, suggesting ministers had misled the public over the dangers of crashing out.

The Brexiters tried to seize back control of their campaign, which has been overshadowed with interventions from Boris Johnson, who described the Chequers plan as a “suicide vest”, as well as his tumultuous personal life.

Johnson, a surprise attendee at the event, ducked questions over whether he would be prepared to launch a leadership bid to prevent Theresa May pushing ahead with her plans. He merely pointed at a colleague and said: “What he said.”

The former Brexit secretary Steve Baker said: “Isn’t the future of this country about more than personalities? This event is not about who the prime minister of this country ought to be, it’s about policy … I’ve not much interest in who the prime minister is.”

Rees-Mogg confirmed that he would vote against the Chequers deal in the Commons but that he hoped the government would not make it a confidence matter, adding that to conflate the two would be a mistake.

The former Brexit secretary David Davis was also among the leading Eurosceptics who crowded into a committee room in the House of Commons on Tuesday to back the plans drawn up by Economists for Free Trade.

The prime minister has challenged the Brexiters to publish their alternative plan to Chequers but ERG members have struggled to reach agreement on how to avoid a hard border in Ireland, a main sticking point in discussions with Brussels.

Rees-Mogg said the ERG would on Wednesday set out a proposed solution to the border problem, which “any reasonable person” would accept. It is expected to include proposals for tax inspectors conducting spot checks in factories on goods for export.

He told the gathering he wanted to strike a deal with Brussels but that the government must not be “snivelling and timorous and fearful” in talks. “If you have got nothing to fear from leaving on a world trade deal basis … then you can say we’ll have a Canada plus-style deal and have a solution to the Northern Ireland problem.”

Baker, a key member of the anti-Chequers campaign who has claimed that 80 Tory MPs would vote against the prime minister’s plans, said: “We are all agreed it would be preferable to leave smoothly into an agreement.”

In response to claims that the UK would not have enough time to reach a free-trade deal he said: “I don’t think anybody is really suggesting that we get down to the last dot and cross on the T on a free-trade deal by exit date. We’re talking about a political statement that, if it’s going to satisfy colleagues in parliament, point to an advanced free-trade deal which leaves us an independent country.”

Johnson, who had not been expected to speak at the event, said Chequers would be “substantially worse than the status quo” for British businesses and that he had a “particular economic objection” to them being tied to the single market.

He again called on May to revert to her Lancaster House proposals. “If only she had stuck to that I think we’d be in a much better position,” he said.