Praising the “very fine people on both sides” when torch-wielding white supremacists and antisemites marched through the streets clashing with anti-racist campaigners. Threatening to veto a ban on the use of rape as a weapon of war. Setting an immigration policy that forcefully separates young children from their parents at the border. The deliberate use of xenophobia, racism and “otherness” as an electoral tactic. Introducing a travel ban to a number of predominately Muslim countries. Lying deliberately and repeatedly to the public.

No, these are not the actions of European dictators of the 1930s and 40s. Nor the military juntas of the 1970s and 80s. I’m not talking about Vladimir Putin or Kim Jong-un. These are the actions of the leader of our closest ally, the president of the United States of America. This is a man who tried to exploit Londoners’ fears following a horrific terrorist attack on our city, amplified the tweets of a British far-right racist group, denounced as fake news robust scientific evidence warning of the dangers of climate change, and is now trying to interfere shamelessly in the Conservative party leadership race by backing Boris Johnson because he believes it would enable him to gain an ally in Number 10 for his divisive agenda.

Donald Trump is just one of the most egregious examples of a growing global threat. The far right is on the rise around the world, threatening our hard-won rights and freedoms and the values that have defined our liberal, democratic societies for more than seventy years. Viktor Orbán in Hungary, Matteo Salvini in Italy, Marine Le Pen in France and Nigel Farage here in the UK are using the same divisive tropes of the fascists of the 20th century to garner support, but are using new sinister methods to deliver their message. And they are gaining ground and winning power and influence in places that would have been unthinkable just a few years ago.

They are intentionally pitting their own citizens against one another, regardless of the horrific impact in our communities. They are picking on minority groups and the marginalised to manufacture an enemy – and encouraging others to do the same. And they are constructing lies to stoke up fear and to attack the fundamental pillars of a healthy democracy – equality under the law, the freedom of the press and an independent justice system. Trump is seen as a figurehead of this global far-right movement. Through his words and actions, he has given comfort to far-right political leaders, and it’s no coincidence that his former campaign manager, Steve Bannon, has been touring the world, spreading hateful views and bolstering the far right wherever he goes.

That’s why it’s so un-British to be rolling out the red carpet this week for a formal state visit for a president whose divisive behaviour flies in the face of the ideals America was founded upon – equality, liberty and religious freedom.

There are some who argue that we should hold our noses and stomach the spectacle of honouring Trump in this fashion – including many Conservative politicians. They say we need to be realists and stroke his ego to maintain our economic and military relationship with the US. But at what point should we stop appeasing – and implicitly condoning – his far-right policies and views? Where do we draw the line?

Rather than bestowing Trump with a grand platform of acceptability to the world, we should be speaking out and saying that this behaviour is unacceptable – and that it poses a grave threat to the values and principles we have fought hard to defend – often together – for decades.

I am proud of our historic special relationship, which I’m certain will survive long after President Trump leaves office. The US is a country I love and have visited on many occasions. I still greatly admire the culture, the people and the principles articulated by the founding fathers. But America is like a best friend, and with a best friend you have a responsibility to be direct and honest when you believe they are making a mistake.

In years to come, I suspect this state visit will be one we look back on with profound regret and acknowledge that we were on the wrong side of history.

It’s too late to stop the red-carpet treatment, but it’s not too late for the prime minister to do the right thing. Theresa May should issue a powerful rejection – not of the US as a country or the office of the presidency, but of Trump and the far-right agenda he embodies. She should say that the citizens of the UK and the US agree on many things, but that Trump’s views are incompatible with British values.

History teaches us of the danger of being afraid to speak truth to power and the risk of failing to defend our values from the rise of the far right. At this challenging time in global politics, it’s more important than ever that we remember that lesson.

Sadiq Khan is the mayor of London