The announcement that Jeremy Hunt would be the other finalist in the Tory leadership contest was greeted with a cheer from Boris Johnson’s campaign team and sighs of disappointment among political journalists. Many of my colleagues were salivating over the prospect of a final battle involving Michael Gove. A Gove-Johnson face-off had rich potential to turn into a spectacularly vicious bout of all-in mud wrestling between the two Brexiters. A Hunt-Johnson contest appears, at least at first sight, to offer a much less compelling spectacle, leading to a much more predictable ending.

“God knows how we got that many,” remarked a member of the Hunt campaign team when their candidate just squeaked into second place in the ultimate ballot of MPs. We don’t have to go to God for the answer to that one. As I predicted they would in this space last week, the Johnson team moved around some of their votes to get Mr Hunt into the final because he is their preferred opponent.

On the face of it, his chances of winning look as slight as Afghanistan’s hopes of lifting the Cricket World Cup. His rival has the support of more than twice as many MPs. Mr Johnson is overwhelmingly more popular with the Tory membership, an audience that is predominantly white, male, southerly, affluent, very Brexity and much keener on the former foreign secretary who campaigned to leave the EU than the current holder of the office who did the opposite.

What can Mr Hunt do about this? If his main interest is self-preservation, the cowardly option is to bow to what may seem like the inevitable and not endeavour to make it a proper contest. We will know he is taking this course if he goes easy on his rival, pulling his punches in the hope that not jabbing at the other man’s many vulnerable flanks will be rewarded with a plum post in the Johnson cabinet. We must hope that Mr Hunt possesses more self-respect than this; that he wants to do more than spend the next four weeks tramping around the country being the train-bearer to King Bozza as he swaggers towards a coronation.

This contest is an opportunity to kick the tyres, inspect the engine and check the brakes of the men who want to be Britain’s next prime minister. It is a deeply unsatisfactory process, from which the vast majority of the country are disenfranchised, but it is the only process there is. To make it a meaningful test, Mr Hunt must prove that he is tougher than he looks and make good on his promise to give the other man “the fight of his life”.

He won’t prosper by trying to imitate his rival. He will never tell better jokes. He will never make more fantastical promises. He will never match the other man’s gift with the flamboyant phrase and the outrageous untruth. He did himself no favours last year when he made a Johnsonian kind of remark about the EU resembling the Soviet Union. There’s no mileage for Mr Hunt in trying to be more Johnson than Johnson.

One of Mr Hunt’s tasks is to sit the Tory party down, tell it to breathe deeply and invite it to have a proper think

The former mayor of London will sell himself as the man who can make Tories feel good about themselves. Mr Hunt can’t contest at that level so he should campaign as the candidate who invites Tories to think soberly about themselves, their country and the qualities that ought to be required of a prime minister.

He is entitled to make character an issue. Not as in personality, but as in moral character. The Tories have a history as a party of falling for scoundrels who present as “lovable rogues”. This has always been an integral element of Boris Johnson’s popularity with the Tory grassroots. But do they really want to hand Number 10 to someone quite this roguish? And is he actually all that lovable? The spotlight has been swivelled on to his torrid personal life by the episode in the early hours of Friday morning at his girlfriend’s home. Neighbours who called the police heard banging, slamming, shouting, screaming, swearing, stuff getting smashed and Carrie Symonds complaining that a sofa had been ruined with red wine: “You just don’t care for anything because you’re spoilt. You have no care for money or anything.”

That’s an unattractive character reference from someone who goes to bed with him. It fits with a theme of his life: that the least flattering descriptions come from those who know him best. Sir Max Hastings, who employed him at the Daily Telegraph, describes him as “a gold medal egomaniac. I would not trust him with my wife nor – from painful experience – my wallet... He is also a far more ruthless, and frankly nastier, figure than the public appreciates.”

Politicians can change their hairstyles, waistlines, tax policies, views on transport projects and sexual partners, but they can’t change their essential character.

Mr Hunt will be wary of getting very personal, but he doesn’t have to get into his rival’s rackety private life to make the case that a Johnson premiership would be a hair-raising gamble with both the future of the Tory party and the future of Britain. Of course, Tory members probably know this already and perhaps they do not care. An eye-popping poll suggests that a majority of them will sacrifice almost anything in order to get Brexit, including the United Kingdom itself. They’d see Scotland and Northern Ireland ripped out of the UK rather than give up on Brexit. A large majority would quit the EU even if it inflicted “significant damage” on the economy and “destroyed” their party. This is the view of people who call themselves members of the Conservative and Unionist party.

So one of Mr Hunt’s tasks is to sit the Tory party down, tell it to breathe deeply and invite it to have a proper think. Are they really prepared to contemplate the ruination of so many things they once cherished in pursuit of an ultra’s version of Brexit? Is a party that once prided itself on being sensible really prepared to take a wild gamble on a Johnson premiership?

One duty that falls on Mr Hunt is to use the next month to direct fierce scrutiny at his rival’s often shifting and contradictory propositions about Brexit. Boris Johnson promises that he can negotiate a better deal and, if he can’t, Britain will be out “come what may” on 31 October. How exactly is he going to do a deal by Halloween with an EU that says it won’t reopen the withdrawal agreement? If he is in possession of a magical solution to the Irish border conundrum, why didn’t he reveal this masterplan to his colleagues during the two years when he sat in the cabinet as foreign secretary? How is he going to take Britain out of the EU without a deal when there is no mandate from the people for a crash-out Brexit and no majority for that outcome in parliament? He now echoes Nigel Farage in suggesting that Britain has a pain-free option called “leaving on WTO (World Trade Organisation) terms”. If that is a credible plan of action, why was it not aired by him or his fellow Brexiters during the 2016 referendum? Could it be because it is just another fantasy that doesn’t withstand a moment of examination by anyone who understands how trade agreements work?

These are questions that need asking and pressing, asking again and pressing again, until Mr Johnson runs out of unicorns to ride and places to hide. Mr Hunt should take a leaf out of Rory Stewart’s campaign book and make himself the honest candidate who asks the hard questions. He will have to be the one prepared to tell his party some truths about Brexit and get it to face the realities of its position.

This can get him in range of his opponent’s greatest vulnerability. Boris Johnson’s supposed talent as a campaigner is his big attraction to Tories. It comes attached to the big risk to them that he could tumble the country over the cliff and his party into an annihilating election. In that poll of Tory activists, there was one idea that they loathed more than giving up on Brexit. That was a Jeremy Corbyn government.

The odds are stacked against Mr Hunt. But even if he is defeated, he can fail honourably by making this a contest, not a coronation. He will be doing a vital service to both his party and the country if he interrogates the character, punctures the fantasies, nails the evasions and unravels the deceptions of his opponent. He should strive to compel a little more honesty from the other man. If Jeremy Hunt can do that, he might even make Boris Johnson a bit fitter to become prime minister.

• Andrew Rawnsley is Chief Political Commentator of the Observer