There are not many laughs to be had from international diplomacy, but US foreign policy in the age of Donald Trump provides a grim kind of comedy all the same. This week the world’s diplomats allowed themselves a chuckle at the risibly inconsistent US approach to Russia, in which the State Department whacks Moscow with sanctions even as the president murmurs sweet nothings into the ear of Vladimir Putin.

When it comes to Russia, the US has become the Jekyll and Hyde superpower. Just three weeks ago, Trump stood next to Putin in Helsinki, unable to utter so much as a word of criticism of the Russian dictator who, a vast body of evidence shows, acted to subvert the American democratic process in 2016. And yet on Wednesday the US announced new sanctions on Moscow as punishment for the attempted assassination of Sergei Skripal and his daughter Yulia in Salisbury with a lethal nerve agent.

What a joke, foreign ministry types will be saying to themselves. The Trump administration is divided against itself, a White House spokesperson only formally endorsing the State Department move a full two days after it had happened. On Friday it emerged that the president’s own national security adviser, John Bolton, plotted with European diplomats to rush through a new Nato strategy document when Trump wasn’t looking – in order to deny him the chance to wreck it and, especially, to soften its tough stance on Russia.

But UK diplomats should resist the smug laughter. For watching the bizarre, contradictory contortions of the US’s Russia policy – Trump pulling one way, the rest of his administration the other – invites an uncomfortable question about British policy. Isn’t the UK guilty of a similar contradiction, in fact one that’s even worse?

Why has Trump stayed unusually quiet on US sanctions against Russia? Read more

Britain has, of course, been tough on the use of a Russian-made nerve agent on the streets of a British city. Indeed, one of Theresa May’s rare diplomatic successes was in persuading a host of allies to follow the UK lead in expelling Russian embassy personnel following the Skripal attack. In this, May is in step with the US State Department.

When it comes, however, to evidence of Russian intervention in Britain’s democratic process, specifically the European referendum of 2016, May is more like Trump: remarkably, unaccountably relaxed.

This week the Guardian added more colour and detail to the picture that, along with the Observer, it has been revealing for months. Specifically, it published details of the lucrative goldmining deal that was dangled by the Russian ambassador in front of Arron Banks, the main donor behind Leave.EU, in the lead-up to the Brexit vote. Readers can now see for themselves the tempting PowerPoint presentation Moscow made to Banks – opening with a slide of shimmering gold bars, complete with Cyrillic engraving, alongside a Russian flag.

Play Video 1:32 All of Trump's backflips on Russian interference – video report

At the very least, you would think the UK government might be curious as to why Putin’s top diplomat in London would favour Banks not only with multiple meetings – four at last count, though Banks used to say they had met only once – but with such exclusive “opportunities not available to others”, to quote the pitch document. Banks says he didn’t take up the golden offer, which included a promise of support from a Kremlin bank, much as Trump says the Trump Tower meeting between his son and Russian representatives promising dirt on Hillary Clinton “went nowhere”. But that is hardly the point. Given that Banks has never explained the precise source of the £9m he gave to the Brexit campaign – the largest single donation in UK political history – the fact that the Russians lavished such preferential attention on him requires explanation, starting with: what exactly did they expect in return?

That Russia was ready to do its bit to make Brexit happen is already well-established. We have had for nearly a year the documented proof that the Kremlin ran a social media campaign through the Internet Research Agency, its troll farm in St Petersburg, using more than 400 fake Twitter accounts to push for a British exit from the EU.

Where, though, is the outrage from the British government? Even US Republicans acknowledge that Russian activity in 2016 constituted an attack on American democracy, on the right of American voters to make their own decisions free of foreign intervention. Where is the equivalent condemnation, or at least demand for answers, from May and her ministers? Instead her position is oddly akin to the Janus-faced stance of the Trump administration: noisy about Salisbury, hushed about Russian sabotage of the 2016 vote.

US to impose sanctions against Russia over Salisbury nerve agent attack Read more

In a way, the UK situation is worse. The US is at least conducting an inquiry into Moscow’s campaign to sway the ballot two years ago, thanks to the investigation led by former FBI director Robert Mueller. True, that effort is opposed by Trump himself – who on Thursday called it “an illegally brought Rigged Witch Hunt” and who may eventually move to shut it down – but it has already borne fruit, including charges against a dozen Russian intelligence officers accused of interfering in the 2016 election. We still have no such probe in Britain, not by the police or the National Crime Agency, let alone a judge. Nothing.

For Trump, the motive for opposing Mueller is obvious: he fears that to admit Russian subversion would be to cast doubt on his own electoral legitimacy. For May, the calculation is not dissimilar: hers is now a Brexit government, and she dares do nothing that might undermine the so-called “will of the people”.

But the result is the same. The UK government, like Trump’s, faces two contradictory ways on Russia – tough on one attack by Moscow, bizarrely forgiving of another. You don’t have to believe that it was Russian help that won it for Trump or Brexit: there were other, deeper factors. But May’s silence in the face of an attack on this country’s democracy – indeed, on its sovereignty – is no more defensible than Trump’s. The Americans are conducting a full-scale inquiry. Where is ours?

• Jonathan Freedland is a Guardian columnist