As commentators line up to debate the character and personality traits of the two men running for the Tory leadership – and by default our prime minister – there is only one question on my mind: how credible are the details of how and when they can deliver or resolve Brexit?

This does not appear to be a question 84% of Conservative party members are remotely bothered with, as they would prefer the fantasy of an immediate “clean Brexit”. They welcome their witching hour of 11pm on 31 October becoming Independence Day, as if it’s some sort of Hollywood blockbuster, with no deal.

If only will was reality. There is a raft of legislation required even in a no-deal scenario – for example bills on agriculture, fisheries, financial services, trade and immigration. So, too, the vexed question of the Irish border. Boris Johnson, like an overexcited puppy when interviewed by the BBC’s Laura Kuenssberg this week, grabbed this bone and enthused about “abundant, abundant technical fixes that can be introduced to make sure that you don’t have to have checks at the border”. Johnson is not one to worry about details, given the fact that in January Sabine Weyand, the EU’s deputy negotiator, said: “We’ve looked at every border on this Earth, every border the EU has with a third country – there’s simply no way you can do away with checks and controls.”

Then there is the clause in the European Union (Withdrawal) Act 2018. Section 10, on the subject of the Irish border, states that nothing in this act “authorises regulations which … diminish any form of North-South cooperation provided for by the Belfast agreement”. This is likely to mean that the Northern Ireland backstop will stay in place until MPs reach an agreement that honours the UK’s obligations under the Good Friday agreement.

I can hear the naysayers now – we are Great Britain, we can leave with a clean Brexit and a smooth transition to World Trade Organization (WTO) terms under which the rest of the world trades. Yes, Britain is a signatory to the WTO in its own right – but there are no WTO terms that apply specifically to the UK, as we have been operating under the EU’s umbrella for decades.

To deal directly under WTO terms will require us to have something called a schedule of tariffs, which applies tariffs to all imports into a country as well as quotas for a certain amount of tariff-free goods. Brexiteers such as Bernard Jenkin MP say we can simply rely on “default terms” or the EU’s schedule of tariffs. But that suggestion has already, understandably, been blocked by many of the 164 WTO members. Why would they allow the UK to take advantage of the negotiating position of a large global trading bloc such as the EU, when they themselves can’t? Unless Britain can set up emergency cover by using the EU schedule or our own schedule without formal approval, we will enter uncharted territory on the morning of 1 November, as no deal means no transition period. Again, Johnson thinks this is “tosh”. He can magic this, too – an implementation period not attached to a withdrawal agreement, but agreed by the EU anyway – even though he has not spoken to a single person on the EU side about this.

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

Johnson will say we can be like Australia or New Zealand or Norway, conveniently forgetting that Australia has trade agreements in place with more than 17 countries, including the US, China, Japan, Singapore and Malaysia, and deals with another 20 countries signed and in the pipeline.

I do not doubt that there are many countries that will wish to trade with the UK post-Brexit, but understandably they will wait to see what the UK’s ultimate relationship with Europe will be. WTO members will be watching Britain’s diplomatic behaviour closely. How the new prime minister and his government conduct themselves, especially if they refuse to pay the £39bn bill, will have a serious impact – and possibly make us devoid of international goodwill.

Trade would not stop, but there will be legal uncertainty, tariffs and barriers, and protectionism from other countries. In some sectors, such as meat and dairy, tariffs as high as 97% would result in British farmers who export lamb and beef seeing their prices double to uncompetitive levels. Imports of animal feed and fertilisers could also face tariffs, so farmers’ costs will increase, squeezing margins in the face of falling sales and no subsidies. This would affect chemicals and machinery parts too, which operate on a “just in time” basis, and also labour. A similar story would unfold across other sectors, with everyday imports we depend on – life-saving drugs, radioactive isotopes for MRI scans, medical equipment, epilepsy drugs, contact lenses, electricity, petrol, even milk – being hit.

Most politicians stay quiet on the fact that we are an 80% service economy. The WTO/Gatt regime into which this would fall would mean other countries being able to impose barriers, such as requiring doctors, accountants or architects to requalify. The financial services sector, which has been world-leading, and the UK aviation services sector, the third largest in the world, would be hugely affected: the EU has a competitive single market for air transport.

Meanwhile, though the prime minister will change, the arithmetic in parliament won’t. And there will be just 20 sitting days to the end of October to resolve the hornets’ nest of issues – and no one on the EU side of the table to renegotiate with until mid-November at the earliest.

But let’s not be bothered with mere details. Who needs policies and practical solutions – sheer force of personality will win the day. Why worry that we would be poorer and less safe than we are today?

• Gina Miller is a businesswoman and transparency activist