It is traditional, on the eve of a party’s annual conference, to highlight the challenges facing the leader. Convention dictates that Theresa May’s performance in Birmingham next week be advertised as the most important of her life. But those cliches are almost redundant given the scale of the mess the Conservatives are in and the improbability of Mrs May describing a remedy.

The prime minister is handling Brexit badly, and the course of action being urged by the most influential Tory faction would make things worse. On Friday Boris Johnson, the former foreign secretary, published a “six-point plan” to challenge Mrs May’s Chequers blueprint. Its essential features are denial that the single market has been valuable to the UK economy, pretence that the benefits of EU membership are available from the outside, and faith in a Canada-style free-trade deal, although the shortcomings of that model are well documented. It erects barriers where currently there are none and, as applied on the island of Ireland, envisages new border controls that the government has pledged not to apply.

Mr Johnson wishes away those problems with a prefix: his plan is not just Canada, but “super-Canada”. To remove concerns around Ireland he proposes reneging on the December 2017 interim Brexit deal that was signed in Brussels when he was in the cabinet. Here is a man positioning himself to replace Mrs May, recommending betrayal of an existing agreement as the first step towards signing a new deal with the very same partners. That is vandalistic anti-diplomacy in the Donald Trump mould. It demeans Britain that Mr Johnson was ever foreign secretary and that his party takes him seriously as candidate to be prime minister.

A strong leader would deride the vacuity of her Tory rivals and their nonsensical plans, but Mrs May’s position is pitiable. Her Chequers plan is poorly understood in the country, unpopular with Tory members, and has been rejected in its current form by the EU. Even if, by some unlikely feat of negotiating prowess and parliamentary arithmetic, Chequers becomes the final Brexit deal, it would be inferior to the terms Britain now enjoys as a full EU member.

The non-existence of options better than the one rejected in the 2016 referendum is an urgent truth that has yet to be properly expressed during this party conference season. Labour has come closer to it than the Tories, largely as a result of grassroots pressure from pro-European members and campaigners urging another referendum vote. Jeremy Corbyn’s acceptance that “all options” are on the table demonstrates the necessary capacity for pragmatism. But the opposition’s emphasis on a general election has the effect of deferring engagement with the same hard choices and uncomfortable messages that the prime minister has persistently avoided.

Around the fringes of the Conservative conference there will be pockets of moderation. In the shadows, the gravity of the impending crisis may be discussed with reference to rational economic judgment, free from ideological zealotry. Such discussion will include the practicalities of extending the article 50 negotiating period; potential alliance with Labour MPs to form a majority bloc in favour of a much softer Brexit; or legislating for a referendum with remain as one of the options. None of those ambitions is easy to achieve, but simply being possible and not wildly inimical to the national interest distinguishes them from the noisier Brexit discussion conducted by Eurosceptic hardliners and many ministers.

It is not too late for Mrs May to join the serious conversation and distance herself from the reckless and ruinous one. It is not too late for her to address the British public over the heads of her party’s anti-Brussels ultras, standing up to fanatics whose denial of diplomatic and economic reality is making Britain a pariah in Europe. Following the demands of the most Eurosceptic fringe is a strategy that has not served any Tory leader well. Perhaps, in this last conference before Britain is due to leave the EU, Mrs May could break with party tradition and address the European question not as it is imagined by many Conservatives but as it truly affects the whole country.