It seems we learn nothing from history, even recent history.

Donald Trump and Kim Jong-un should already have alerted us to the dangers of leaders with bad haircuts.

Yet the end of the month of May also spelt the end of Theresa May. The race to replace her officially began this week – though it feels as if it unofficially began months ago. And the runaway favourite is the one with the runaway hair: comedy toff, serial adulterer and insulter of foreigners Boris Johnson.

The man who looks certain to be our next prime minister is the former foreign secretary who described Africans as “piccaninnies with watermelon smiles” and Muslim women as “bank robbers”, and said that Libya would be great “once they’d cleared all the dead bodies away”.

He was quite ready to insult people closer to home too, writing in reference to the Hillsborough tragedy that Liverpudlians “wallow in their victim status”.

Then there is the cheating on his wife and the lies. During May’s local elections he tweeted that he had just been to the polling station to vote Conservative and urged his followers to do the same.

It was swiftly deleted when some pointed out that where he lives, in central London, there were no local elections.

That was just the most recent. The most notorious came on the side of the Brexiteers’ bus during the referendum campaign.

It bore the falsehood: “We send EU £350m a week. Let’s fund our NHS instead.”

The figure was an immense exaggeration. It ignored the UK’s rebate from the EU – the discount we get. It also ignored the money the EU sends to Britain to fund projects and support farmers here.

That’s not to mention the wider economic benefits that come from membership, like jobs.

But Brexit will have a noticeable impact on the NHS. It will seriously damage our health.

Don’t take my word for it. Ask a doctor.

Doctors and nurses are against leaving the EU by a margin of three to one, and it’s easy to see why.

There has been a sharp drop in the number of nurses and midwives from other EU countries working in our health service since we voted to leave. Around 5,000 have quit within the last two years.

Foreign nationals aren’t the ones ahead of you in the queue for a hospital bed. They are the ones standing beside the bed, looking after you.

The state of the NHS is not an argument for Johnson and his no-deal Brexiteers. It’s a powerful argument for remain.

If the Brexiteers are so convinced that they’re right, then why don’t they hold another referendum and prove it? After all, if it still went their way the remainers would have to admit defeat and the argument would be over.

Is it because they’re frightened that they’d lose? Some elderly anti-EU voters have died since June 2016 and a lot of pro-EU young people who were 16 or 17 then are of voting age now.

The Brexit party may have done well in the European elections. But add up all the votes for pro-remain parties and compare it to those for pro-Brexit ones, and you’ll find that remain had a clear lead.

More pro-European MEPs are going to Brussels from Britain than anti-European ones.

It shouldn’t be a surprise. Many of those who voted Brexit are no longer sure it’s such a good idea. There are 3,000 families in Scunthorpe, where the steel works are under threat, who aren’t convinced of the virtues of Brexit .

The 500 new jobs that tyre manufacturer DMACK had promised to Carlisle are no longer coming, and company founder Dick Cormack is blaming Brexit.

Of course maybe Brexit would win a second referendum. That would settle the argument, and delight Nicola Sturgeon.

It would be the beginning of the end of another political and economic union, the United Kingdom.

Scotland would leave the UK at the earliest opportunity in order to rejoin the EU. Northern Ireland and Wales wouldn’t, but their positions in the UK – and the point of the UK as a whole – would begin to be questioned.

Johnson, or whoever replaces May, will not only be remembered as the prime minister who presided over Brexit. He or she will be remembered for presiding over the break-up of Britain.

And Cameron, who recklessly held the referendum in the first place, will share the blame. I hope he’ll be satisfied by his place in history.