Boris Johnson would be able to ignore parliament’s efforts to stop a no-deal Brexit and blame the EU if it refuses to give the UK a better deal, one of his supporters has said.

Dominic Raab, who is backing the frontrunner after being knocked out of the leadership contest, said any motion from MPs against a no-deal Brexit would have “zero legal effect” and could be overridden.

He also said it would be “the EU’s fault” if Britain leaves on World Trade Organization terms because it was possible to strike a better Brexit deal before the end of October if there was sufficient political will.

In an interview on BBC Radio 4’s Today programme, Raab argued that leaving the EU without a deal would not be a problem, partly because the general agreement on tariffs and trade (Gatt) could be applied to create a standstill on tariffs with the EU.

Mark Carney, the governor of the Bank of England, and Liam Fox, the trade secretary, have said it is not possible for the UK to trigger this unilaterally. But Raab said Carney was not a lawyer and claimed that “legally it could be done and the question is whether there is the political will”.

Q&A What is Gatt XXIV or article 24? Show Gatt XXIV, or article 24 of the General Agreement on Tariffs and Trade is a piece of international trade law from 1947 which pre-dates the existence of the World Trade Organization (WTO). If the UK leaves the EU without a deal, then by default it means the end of tariff-free trade between the two parties. Some supporters of a no-deal Brexit have claimed that the UK can use Gatt XXIV to implement a period of up to 10 years where trade between the UK and EU continues under existing arrangements while a comprehensive free trade agreement (FTA) is negotiated.

Under the WTO’s most-favoured nation rule (MFN), if the UK offered tariff-free access to the UK market to the EU, it would also have to do so to any other trading partner with which there was not an already established FTA. With Gatt XXIV, Brexiters say, the UK can maintain its existing zero tariffs and quotas EU access as part of a ‘standstill’ arrangement.

However to invoke Gatt XXIV, both the UK and the EU have to agree an ‘interim arrangement’ leading towards a FTA within the 10-year time limit - and that agreement has to meet the conditions and approval of the WTO. The UK cannot invoke article 24 unilaterally, and even if it could, it only applies to goods, and not to services. In 2017, services made up 79% of the UK’s economic output.

In previous cases where the article has been used, the two sides had a deal in place, and it was used as part of a process of implementing new trade arrangements. It has never been used to replicate something of the scale and complexity of the EU and the UK’s trading relationship - and if the UK truly leaves the EU with no deal, then there is no interim arrangement to apply Gatt XXIV to.

Martin Belam

He batted away suggestions that parliament would find a way to stop a no-deal Brexit on 31 October, arguing it was necessary to end the “pantomime” over leaving the EU.

Raab claimed there would be only a “vanishingly small” number of Conservative MPs willing to vote down their own government to prevent no deal, as they would conclude that the risk of a Jeremy Corbyn government was greater.

In a separate interview, Rory Stewart, another former Tory leadership contender, said he would vote with opposition parties to prevent the UK leaving the EU without a deal on 31 October. But he would not go so far as vowing to vote down the government to prevent no deal, as “a dozen or so” Conservative MPs are prepared to do according to the defence minister Tobias Ellwood.

Stewart said: “I would definitely vote against a Conservative government to stop a no-deal Brexit. I wouldn’t vote to bring down a Conservative government. I don’t want Jeremy Corbyn to be prime minister. I would be working with colleagues to use the legislative instruments in order to stop a no-deal Brexit.”

This month, the Tory MP Oliver Letwin said parliament had run out of options for preventing a no-deal Brexit, after a motion he helped to table aiming to tie the next prime minister’s hands on the issue was defeated by 11 votes.

But Stewart, who voted with the government in that vote, insisted parliament had not exhausted all options to prevent no deal.

Stewart, who said he was backing Johnson’s opponent, Jeremy Hunt, said: “Parliament is against no deal. It is only the legal default because parliament made it the legal default. Parliament can unmake it the legal default. There are many, many opportunities in legislation that have to brought forward, that could be amended in order to stop a no-deal Brexit.”

Stewart appeared resigned to accepting that Johnson would become the next prime minister. But he said Johnson would let all his supporters down because he would not be able to stick to his promises.

He said: “Boris is pretending that he has a magic solution where he can take people out [of the EU without a deal] and is not going to damage them at all, and it’s going to be terrific. That’s very clever, because it is resonating with people. But the reality is that he can’t do it and he’s going to let people down.

“He’s going to let down the remainers that support him, who somehow think he’s going to finagle it. He’s going to let down the hard Brexiteers because he’s not going to come out on 31 October. The problem is that on 1 November he’s going to end up with a lot of disappointed and frustrated people.”