Early this summer, a national newspaper published a string of curious articles. Under the logo Universal Credit Uncovered, the features promised readers of the Metro the truth about this most notorious of all benefits. The series began with a giant advert wrapped around the cover of the paper, coupled with a four-page spread right in its centre, and continued week upon week for nine weeks. Launched by the Department for Work and Pensions, it was an unprecedented attempt to salvage the reputation of a policy that had been attacked by MPs on all sides, plunged families into starvation and homelessness, and driven councils dealing with the fallout to call for its abolition.

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That suffering across the country was dismissed by the DWP as “negativity and scaremongering” in an internal memo I saw and reported on here weeks beforehand. Signed by three top officials, it described the campaign to the Metro’s 2.5 million daily readers as “very different to anything that we’ve done before”. The civil servants crowed over how readers might be deceived into treating the advertorials as independent reporting: “The features won’t look or feel like DWP or UC [universal credit] – you won’t see our branding … We want to grab the readers’ attention and make them wonder who has done this ‘UC uncovered’ investigation.”

They almost got away with it too – but, tipped off by the Guardian’s reporting, others began an extraordinary fightback. MPs fired questions at Amber Rudd, then the DWP’s secretary of state, while disability activists turned up at train stations, from Swindon to Stoke, and emptied their stands of Metros – with the support of the RMT union. A number were bulk-delivered to Rudd’s offices in Westminster. Other groups, including anti-poverty charities such as Z2K, formally complained to the Advertising Standards Authority that the government was misleading the public. The watchdog was blitzed with 44 complaints (the average for a case is between one and five), and has been investigating the claims since early June. This morning it publishes its findings – and they make quite the starter pistol for the general election.

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Throughout its campaign, the DWP would summarise what it called “Myths” about universal credit and then give readers the “Facts”. The ASA looked at three of the claims – and found they weren’t facts at all. They were lies, told by the government to its own taxpayers.

In big letters, the DWP boasted that “people move into work faster on Universal Credit than they did on the old system”. After poring over the statistics, the ASA has found this claim “did not reflect the evidence … had not been substantiated and was therefore misleading”.

“If you need money,” readers were assured, “your Jobcentre will urgently pay you an advance.” In its ruling, the ASA takes the government to task for not making it clear that this is only a loan and that the vast majority of claimants will have to wait five weeks for their first UC payment.

Finally, the adverts’ claim that “your Jobcentre can pay rent directly to landlords” was again found to be misleading because it only applies to a small number of claimants. The ASA looks at one other charge, that the ads might not be identifiable as such, and while it worries about the “quite small” font that admits this is DWP marketing, only partially upholds it. In total, that’s three clear rulings against the DWP, plus one partially upheld.

It is no small thing for a watchdog to face down the government in such an uncompromising fashion. Yet at the end of its remarkable judgment, there is something even more startling. The DWP is told that in future it must have “adequate evidence to substantiate the claims in their advertising, to include significant conditions [where the claims don’t apply], and to present significant conditions clearly”. The regulator has been forced to advise the Conservative government to tell the truth.

Play Video 2:03 'Absurd and degrading': how universal credit can ruin lives – video

We stand at the edge of an election campaign, a period traditionally marked by half-truths, plausible fibs and outright partisan lies. Yet even amid the discursive sewage that is about to deluge us, this deceit is far different and vastly more serious. First, that campaign was paid for by taxpayers like you and me. The DWP’s own filings show that £225,000 was paid to the Metro to run ads now declared “misleading”, “unsubstantiated” and “exaggerated”. Almost a quarter of million pounds was taken off us to lie to us.

Second, these ads were not devised by Dominic Cummings, or any party operative. As Rudd admitted in a letter this June to a select committee of MPs, “detailed campaign and content planning was taken forward by Department officials”. Under orders to sell the government’s biggest welfare reform this decade, civil servants played fast and loose with the truth. The reputation of the DWP, already badly damaged by countless failures, has taken another huge knock today.

Approached for comment, the DWP has not offered even an apology to the public, merely saying it is “disappointed with this decision”. It further claims that “we consulted at length with the ASA as we created the adverts”. I asked the obvious follow-up: how then do you explain the fact that you’ve breached so many of its guidelines? There was no response. Nor was there any response on whether the DWP is running any more ad campaigns on UC, as several sources both in and out of Westminster have claimed to me.

What the government has effectively done is use public money to gaslight poor people, denying the reality of what has been done to them. In its eagerness to push its gargantuan failure of a welfare policy, it has swept aside the truth and peddled lies. Politicians, campaigners and journalists have all pointed out how Rudd and her DWP predecessor Iain Duncan Smith have done so – and each time we have faced breathtaking defensiveness from a Whitehall department that is meant to be working on our behalf, rather than for the Tories.

So let’s end with some truth on universal credit. Last week in these pages I wrote about Maureen Powell in Colchester, a sick pensioner driven to set up lunch clubs because of the families she sees driven to starvation by universal credit. Tuesday’s report from the Trussell Trust concludes that those claiming the benefit are two and a half times more likely to have to use food banks. And a report last month from the work and pensions select committee reported that women were being driven into “survival sex” to make ends meet because of problems with UC. Among the testimony quoted was one woman who told MPs she was about to be moved on to UC: “I will lose £200 a month. The thought of going into debt and having no money is really frightening. I have children. I will sell my body.”

It takes a particularly rotten government to be confronted with such evidence and think that, rather than fix the policies, it will instead lie about them. But that, apparently, is the one we have.

• Aditya Chakrabortty is a Guardian columnist