I'M struggling with a new and disturbing emotion: a creeping sense of sympathy for Theresa May. Yes, I know. She's a Tory and all that, and was responsible for the “hostile environment” rules on migrants when she was home secretary. She's pretty useless at her job too, combining dogged determination with intellectual rigidity - a dangerous combination in a Prime Minister. Still: she’s a human being, and no one would wish on her the trial she faces at this week's Conservative Party Conference in Birmingham.

Her Chequers deal is toast; Brussels humiliated her at Salzburg; leadership rivals are lining up to replace her; and she is regarded by most Tory members as a traitor to the cause of Brexit. The house journal of thinking Tories, The Spectator, has said she should “go now”, because her leadership has “not just divided, but lobotomised the Tory party”. Ouch.

On Tuesday, before she gives the most important conference speech of her career, she’ll be upstaged by the blond bombshell, Boris Johnson, making a transparent leadership bid of his own. Bets are being taken on what tasteless imagery he’ll deploy. He’s already compared his leader's Brexit policy to “a suicide vest wrapped round the British constitution”. Perhaps this time he'll say “Chequers is Britain's 9/11 with May flying her plane straight at our World Trade Centre”. Or perhaps that she's been “gaslighted by Michel Barnier into allowing Brussels to sexually assault the UK”.

Mrs May will have to grimace and bear it, because she can’t compete with the former Foreign Secretary's star status in the Tory Party. You wonder why she bothers speaking at all. Nothing she can say will reconcile the Tory factions. The Moggites of the European Research Group, want an immediate abandonment of her Chequers “deal”. They have 40-50 MPs who can bring down her government if she persists with attempts to keep Britain in regulatory alignment with the EU single market.

On the other side, Remainers, like the former Home Secretary, Amber Rudd - who seems to have discovered herself since she was sacked - are warning that they too have “around 40 MPs”. They're equally determined to prevent May adopting a Canada-style Free Trade Agreement (FTA.) Indeed, Rudd says she’ll even support a Peoples Vote if Chequers stalls and the Moggites grab the steering wheel.

One of the mysteries of the last two years is why the Remain majority in the Tory party - and in parliament itself – as been so supine for so long. What were they afraid of? A no deal Brexit is patently ludicrous, as last week’s revelations about government plans for possible food rationing confirmed. The “Supercanada” Free Trade Deal promoted by Boris Johnson, in his latest Telegraph epistle, is really not much better. The 2016 Comprehensive Economic and Trade Agreement (CETA) took seven years to negotiate and is manifestly inferior to the arrangement we currently have.

As has been repeatedly pointed out, CETA doesn’t properly cover services, like banking, which account for 80% of the British economy. Nor does it solve the problem of a hard border in Ireland (or in the Irish Sea under the backstop agreement). CETA would inevitably mean the restoration of customs checks and tariffs for thousands of business, if only to negotiate them away again. And of course it would mean non-tariff and regulatory barriers to trade, like those sanitary and phyto-sanitary checks on food exports.

Not a problem, says Boris. Under Supercanada, he says, Britain and the EU could agree “common regulatory standards” to cover services like banking, and there could be mutual recognition of professional qualifications. Well, yes - in an ideal world. But that’s what May’s been trying to do, without much success. Britain and the EU could then simply agree “zero tariffs and quotas”. In whose dreams, Boris? Irish border - “no need for one”, he says. This is puerile. Brexiteers who wanted to “take back control” of our only land border with Europe now say it shouldn’t exist. As the New Statesman's Stephen Bush put it: “Supercanada's unrealistic, Boris is atrocious”.

At best CETA+ is simply reinventing the wheel. The European Single Market (ESM) and the Customs Union (CU) were invented precisely to achieve common regulatory standards, abolish tariffs and eliminating border checks. The complex just-in-time producing supply chains, that have revived the UK car industry, depend on borderless freedom of movement. The Canada deal doesn’t address supply chains, and rules of origin, because there is an Atlantic ocean in between it and the EU. Canada exports a fraction of what we do to the EU, nearly half of British exports.

The single market was devised in the 1980s - and enthusiastically promoted by one Margaret Thatcher – to address an era in which trade in physical goods – things you can drop on your foot – was being replaced by trade in services – like marketing, production design, advertising, TV production, legal services etc.. These intangibles are increasingly what Britain does – and does very well. The EU single market is far from fully achieving common standards for services, but it's well on the way.

The single market allows even small and medium companies in Britain to conduct hassle and cost-free business throughout the biggest and richest trading bloc on the planet. Why would anyone want to leave it for something that even its advocates accept is an inferior arrangement? CETA+ requires heroic wishful thinking that all the regulatory and customs barriers, that come with an old-fashioned free trade deal, could somehow be negotiated away. Yet, as Theresa May has discovered, the EU is not prepared to abandon single market rules just to appease narrow-minded little Englanders who claim, falsely, that the EU is some kind of authoritarian superstate.

Anyway – we already have a Canada-plus Free Trade Deal. It is called the European Free Trade Association, EFTA, and was set up by Britain in 1960 as an alternative to the EU. The EFTA countries, Norway, Switzerland, Iceland and Liechtenstein, then negotiated entry into the EU single market through the European Economic Area. They did this because, while they wished to remain out of the EU, they wanted the benefits of the single market. (Switzerland has a slightly different arrangement but it accepts all the rules of the ESM).

Theresa May realised all this, which is why she tried to renegotiate her way back into the single market by the back door. That's what Chequers is really about – it is a step towards the EEA, albeit a failed one. But CETA goes back in time and also creates a hard border in Ireland. To give the Prime Minister credit, she had the wit to realise this and tried to find a compromise under which Britain would continue in regulatory alignment with the single market to avoid disrupting the UK economy and destabilising Ireland. But the party she leads has become so dysfunctional that it would rather wreck the economy, and divide the UK, than accept that it was wrong about leaving the EU.

So, pity Mrs May this week. She may be a hopeless prime minister and her Chequers deal never really made any sense. But at least she understood the problem.