Please, Theresa May, for the sake of our country’s future, sack Boris Johnson. His continued presence as foreign secretary is a national humiliation. The influence of a leftwing Guardian columnist over the prime minister is, to put it mildly, rather limited. It is up to Conservative members and supporters to come to the conclusion that Johnson’s continued tenure as Britain’s representative to the wider world is a risk to the future of this country.

Political journalist Rachel Sylvester has a piece in the Times today which is as devastating as it is frightening. It languishes behind the paywall, so let me offer some choice highlights. Even Donald Trump’s officials regard Johnson as a joke. “Not a single foreign minister” in Europe takes him seriously. He leaks information given to him confidentially by other governments. He is variously considered by EU states as “totally unreliable”, a “liar” and “dangerous”. He is “ramshackle” and so lacking in concentration span that civil servants have to bypass him and consult his deputy, Alan Duncan, instead.

May only appointed him to manage the internal schism of her chronically divided party

If you are a British citizen, this man is your face to the world. We are in the midst of our greatest national crisis in peacetime, partly because Boris Johnson used his now-diminished star power to support a leave campaign which peddled lies about the NHS and stoked fears about immigration. We are where we are now, and we have to make the best of it. It is beyond reckless right now to have as foreign secretary someone who might seem a bit over the top to be hired as a clown at a kid’s birthday party. The economy, living standards, jobs – the whole shebang is at risk in these negotiations, and we have an Etonian David Brent at the helm. He thinks he’s Winston Churchill, but he’s really just whatever “a chilled-out entertainer” is in Latin.

The charge sheet against Johnson was extensive before he was appointed. Here was a man who described black people as “piccaninnies” with “watermelon smiles”, who suggested Barack Obama’s opposition to Brexit was driven by his “part-Kenyan” ancestry, and who celebrated President Assad’s murderous offensives with “hooray” and “bravo”. As editor of the Spectator, he published articles describing black people as having smaller brains and lower IQs and blaming Liverpool fans for the Hillsborough disaster. If equal marriage should be permitted, he once wrote, then why not allow “three men, as well as two men, or indeed three men and a dog” to get hitched?

He was sacked twice – once by his editor, the other by his then party leader – for lying. He was once recorded having a phone conversation discussing the possibility of beating up a journalist. He was bankrolled by the Barclay Brothers – “chicken feed” is how he described his £250,000 salary – to churn out thesaurus-swallowing defences of the interests of Britain’s shameless booming elite in the Telegraph.

May knew the score and only appointed him as foreign secretary to manage the internal schism of her chronically divided party. Clearly the prime minister is in a weak position when it comes to reshuffling her cabinet – especially the most prominent members. Throwing away your political capital in an unnecessary general election, and reducing yourself to a humiliated laughing stock in the process, somewhat limits your room for political manoeuvre. But really, enough is enough.

Britain is a great country, and it deserves better than being diminished to the status of international punchline. Our European neighbours are starting to treat us like that bloke in the pub at the end of the night who you avoid making eye contact with. It used to be said that Johnson is a bit of a laugh, a joke, or a “LEGEND!” as his most devoted fans in Clapham’s wine bars used to describe him. But the joke is on us. The Tories’ disastrous partisan scheming is responsible for plunging Britain into its current political turmoil. Sacking this clown wouldn’t rectify this Conservative-manufactured mess. But goodness me, it would be a start.

• Owen Jones is a Guardian columnist