Truth or consequences, a parlour game in which players are penalised for dishonesty or wrongdoing, is mostly fun – but it also reflects a broad moral consensus about the unacceptability of lying. This long-held belief is deeply rooted in popular culture. Truth or Consequences was the title of a postwar American TV quiz show whose success was so great that a New Mexico town was named after it. Put simply, and as a general rule, most people expect that if you tell whoppers, you get punished.

Why, then, do so many modern leaders seem to think they can lie and get away with it? A propensity to deny, dodge or disown the consequences of political actions is spreading globally like a toxic virus. There was a time, as David Miliband, the former foreign secretary, argues in this year’s Fulbright Lecture, when public accountability was on the rise. Not any more. In what he calls the age of impunity, “those engaged in conflicts around the world believe they can get away with anything, including murder”.

The past week threw up glaring examples of how leaders lie – cynically, shamelessly and routinely. After a meticulous inquiry, international investigators announced three Russians and a Ukrainian will face murder charges over a ground-to-air missile attack in eastern Ukraine in 2014 that brought down Malaysian Airlines Flight MH17, killing 298 people.

The evidence tying these individuals to Vladimir Putin’s government is overwhelming, based on witness testimony, satellite images and intercepted phone calls to Moscow. The Buk missile launcher used in the attack has been tracked from its base in Kursk to Ukraine and back again. All three Russians worked for their country’s security apparatus. It’s a safe bet they did not act alone.

Kremlin denials nevertheless flow thick and fast. Russia, it says, had no involvement. It had no military personnel in Ukraine and “no opportunity” to participate in the investigation. In other words, Russia is being framed. By any reasonable, factual measure, these protestations are demonstrably, ridiculously false. But contemptuous of the victims and their families’ need for justice, Moscow’s lies just keep on coming.

If a major world power can behave this way, why not lesser leaders, too? Last week Saudi Arabia also waged a bare-faced war on truth after a UN investigator implicated Mohammed bin Salman, the Saudi crown prince, in last October’s murder of the journalist Jamal Khashoggi. Since this scandal first erupted, the kingdom’s preferred defence has been deceit, not decency.

Kremlin denials flew thick and fast. By any reasonable standard, these protestations are demonstrably, ridiculously false

Riyadh’s denials and explanations, proffered in the days following Khashoggi’s disappearance inside the Saudi consulate in Istanbul, were quickly exposed as fabrications. Unfazed, a senior minister once again flatly rejected the UN’s “credible evidence” of the crown prince’s complicity. Its finding that the murder was “an extrajudicial killing for which the state of Saudi Arabia is responsible under international law” was dismissed as “nothing new”.

Is it enough simply to say something isn’t so, even when everybody knows (or strongly suspects) it is? Let’s ask Donald Trump, a serial liar and leading authority on fake news. The US president launched his 2020 re-election campaign in Florida last week. But be aware. Anything he says must be taken with a large shovel of salt. According to White House whopper-trackers, he has made 10,796 false or misleading statements since taking office.

Trump’s porky total rose sharply in Orlando. He lied about the Mueller report (it did not exonerate him) and the “biggest tax cut in history” (it wasn’t). He said “we are starting to remove a lot of troops” from the Middle East even as he deployed another 1,000 to scare Iran. He bragged about his Mexico border “wall”, which mostly doesn’t exist. Truly, Trump would swear the Queen is his bosom buddy if it helped get him votes. In fact, he has.

Trump fans seem not to care that their hero cannot be trusted. And many other countries are similarly infected by the mendacity virus. In China, state media baldly assert that Hong Kong’s street protests are a foreign conspiracy. In Egypt, the regime brazenly denies that its cruel mistreatment of the deposed president, Mohamed Morsi, caused his death in custody. In Britain, Tory prime ministerial hopefuls lie and lie and, in one prominent case, lie low.

What chance the governments or politicians cited above will be punished for their dishonesty, in the courts or otherwise? Saudi, Russian and Chinese citizens do not have much redress when their rulers hide or distort the truth. Moscow, for example, will not allow extradition of the MH17 suspects. And who believes a ranking Saudi royal could be forced to answer for his actions? Yet the quest for truth or consequences cannot just be abandoned.

Last week the chief prosecutor of the International Criminal Court pleaded with the UN security council to use the present upheaval in Sudan to help her finally put the perpetrators of the Darfur genocide in the dock. They have been beyond her reach for 14 years. “Now is the time to act. The victims of Darfur have waited far too long to see justice done,” Fatou Bensouda said.

There is little sign her plea will be answered, by either Sudan’s new military rulers or the major powers. This absence of justice, this hollowing out of truth, this seemingly ubiquitous refusal to face or impose consequences is partly what Miliband meant by an arrogant new age of impunity. “Constraints on the abuse of power are being weakened internationally and nationally,” he says. This cannot continue. Those who can must speak out plainly – and truthfully – or be complicit in a world of lies.