It’s Friday lunchtime and Boris Johnson is in Oldham. He’s live on Sky News, speaking to supporters in front of his Tory battle bus. During a speech lasting no more than 10 minutes, viewers learn that he is building 40 new hospitals. Sounds good. But it’s a lie that has already been exposed by fact-checkers, including the website Full Fact.

The prime minister tells Sky viewers that “20,000 more police are operating on our streets to fight crime and bring crime down”. This assertion is misleading in a number of ways. Recruitment will take place over three years and do no more than replace the drop in officer numbers seen since the Conservatives came to power in 2010.

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Sky viewers are then informed by Johnson that Jeremy Corbyn “plans to wreck the economy with a £1.2 trillion spending plan”. Labour’s manifesto hasn’t been published, let alone fully costed. Johnson’s £1.2tn is a palpable fabrication. As Full Fact concluded: “Many of the figures behind this estimate are uncertain or based on flawed assumptions.”

Johnson then goes on to say that the Labour leader “thinks home ownership is a bad idea and is opposed to it”. I have been unable to find any evidence of Corbyn expressing this view. Perhaps Johnson is referring to the floated Labour policy that would give “right to buy” to private tenants. The policy, which was only ever supposed to target the wealthiest landlords, has since been dropped and, according to the Financial Times, will not appear in the party’s manifesto.

Johnson then told his TV audience that Corbyn “wouldn’t even stick up for this country when it came to the Salisbury poisonings” and that he sided with Russia. Another obvious lie. In the aftermath of the poisonings, Corbyn wrote in the Guardian: “Either this was a crime authored by the Russian state; or that state has allowed these deadly toxins to slip out of the control it has an obligation to exercise.” The Labour leader also stated that the Russian authorities must be held to account.

Meanwhile, Johnson’s own government is refusing to publish a report into Russian interference in British politics amid reports that a number of wealthy businesspeople with links to Vladimir Putin have donated generously to the Tory party.

At the end of his speech, the Sky News presenter, Samantha Washington, strikingly made no attempt to challenge or correct any of Johnson’s false statements. This was just the latest example among many of the British media letting Johnson get away unchallenged with lies, falsehoods and fabrication.

Welcome to the Conservative party election campaign. I have been a political reporter for almost three decades and have never encountered a senior British politician who lies and fabricates so regularly, so shamelessly and so systematically as Boris Johnson. Or gets away with his deceit with such ease.

Some of the lies are tiny. During a visit to a hospital he tells doctors that he’s given up drink, when only the previous day he’d been filmed sipping whisky on a visit to a distillery. And sips beer on film the day after in a pub.

Facebook Twitter Pinterest ‘He tells doctors during a visit to a hospital that he’s given up drink, when only the previous day he’d been filmed sipping whisky on a visit to a distillery.’ Boris Johnson during a visit to Roseisle distillery. Photograph: WPA Pool/Getty Images

But many are big. Johnson repeatedly claims that Britain’s continued membership of the EU costs an extra £1bn a month. False.

He told activists that the Tories were building a new hospital in the marginal seat of Canterbury. False – and shockingly cynical.

He told Michael Crick that during the EU referendum campaign, “I didn’t make remarks about Turkey, mate.” He did.

On his potential conflict of interest over his friend Jennifer Arcuri, who received £11,500 from an organisation he was responsible for as London mayor, Johnson said: “Everything was done with complete propriety and in the normal way.” We now know he failed to declare this friendship, and is being investigated by the Independent Office of Police Conduct.

These lies point to a systemic dishonesty within Johnson’s campaigning machine. His party deliberately doctored footage of the shadow Brexit secretary, Keir Starmer, to make it look as if he was at a loss for words when asked about Labour’s Brexit position. In fact, Starmer had answered confidently and fluently. The video was a deliberate attempt to mislead voters. And when Piers Morgan tackled the Tory chairman, James Cleverly, on the issue, he refused to accept he’d done anything wrong, let alone apologise.

Beyond Johnson and his cabinet, there are unscrupulous Tory briefers working behind the scenes. One of them told journalists last week that Johnson was going to accuse Corbyn of political “onanism” the following day. It was gleefully reported in some papers, but Johnson did not use the phrase in his speech. Political correspondents are being taken for a ride by the Downing Street machine, which is as contemptuous of newspaper readers as it is of the truth.

As someone who has voted Conservative pretty well all my life, this upsets me. As the philosopher Sissela Bok has explained, political lying is a form of theft. It means that voters make democratic judgments on the basis of falsehoods. Their rights are stripped away.

This matters more than ever because this election is the most important in modern British history. If Johnson wins, Britain will leave the EU within a matter of weeks and Johnson himself will serve a five-year term as prime minister.

In theory Johnson should not be able to get away with this scale of lying and deceit. In a properly functioning democracy, liars should be exposed and held to account. But that isn’t happening. As with Donald Trump, for Johnson there seems to be no political price to pay for deceit and falsehood. The mainstream media, as Washington’s response to Johnson’s speech shows, prefers to go along with his lies rather than expose them.

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Recently the hugely experienced broadcaster Andrew Marr allowed Johnson to go unchallenged in saying the Tories “don’t do deals with other political parties”. What about the coalition government with the Liberal Democrats in 2010? Or the £1bn “confidence and supply” deal struck with the Democratic Unionist party just two years ago? Marr let Johnson get away with it. So do many others.

A big reason for Johnson’s easy ride is partisanship from the parts of the media determined to get him elected. I have talked to senior BBC executives, and they tell me they personally think it’s wrong to expose lies told by a British prime minister because it undermines trust in British politics. Is that a reason for giving Johnson free rein to make any false claim he wants?

Others take the view that all politicians lie, and just shrug their shoulders. But it’s not true that all politicians lie. Treating all politicians as liars gives a licence for the total collapse of integrity of British politics, a collapse that habitual liars such as Johnson are delighted to exploit. The British media is not holding him to account for his repeated falsehoods. It’s time we journalists did our job, and started to regain our self-respect.

• Peter Oborne is a journalist, commentator and author. His website about the lies, falsehoods and misrepresentations of Boris Johnson is at https://boris-johnson-lies.com