The Article 50 letter is on its way to Brussels. Theresa May's team have been desperately trying to get the details right. Tone is everything, they say. We need to set the right attitude from the start.

If only they thought this way before. In the weeks after the referendum result, European leaders were shell shocked. They needed reassurances. They needed to know that Britain intended to pursue the divorce cautiously, respectfully and with as much consideration for their own project as its own.

British ambassador to EU Sir Tim Barrow arrives at European Council building to deliver Article 50 letter #BrexitDay https://t.co/6jIwKBuWuw pic.twitter.com/6iJ4G4DQIF — ITV News (@itvnews) March 29, 2017

You could hear the kind of language we needed from chancellor Philip Hammond this morning. "What we're seeking to do here is negotiate a deep and special relationship with the European Union," he told Radio 4 today. "We can't cherry pick. We can't have our cake and eat it."

How useful this would have been months ago. Instead, European leaders were forced to watch in disbelief as British ministers claimed they could negotiate trade with individual EU member states, which is illegal, or that they could scrap free movement and stay in the single market in current conditions. They were used to sensible British officials in Europe finding compromise positions on difficult issues, making promises and delivering on them. Now, they had been replaced by Ukip clones, shouting out angry, entitled, ignorant nonsense. The Boris Johnson maxim of cake and eating it became the new definition for the British approach to Europe.

Then came the Amber Rudd speech suggesting the government would force companies to publish lists of foreign workers they employed. It was quickly dropped, but the mood in Europe changed and never went back. They were not just facing a break from a political project anymore. They were facing a challenge to the entire liberal order, a reactionary nativist surge in the West which could destroy the institutions built since the Second World War.

May's visit to Washington cemented this impression. The photo of her and Donald Trump holding hands did more damage than she could imagine. Her obsequiousness and plain desperation for a post-Brexit trade deal contributed to an impression that Brexit was the Trump vanguard in Europe. It had to be slapped down, as Le Pen and Wilders and Alternative for Deutschland had to be slapped down. May allowed herself to be associated with an out-and-out anti-European American president just ahead of talks with Europe. It was another catastrophic error of strategic judgement.

The rhetoric of ministers, Tory backbenchers and the eurosceptic press fuelled Europe's suspicions. Constant World War Two metaphors were used and even where they weren't, the language was so aggressive and self-interested that it hardened the backs of anyone tempted to give Britain a better deal.

The debate in the UK became hermetically sealed and disconnected from reality. By the time May gave her Lancaster House speech laying out her Brexit plan, she thought it moderate and centrist. In fact, it offered Europe nothing. There was not one area where it showed how their own situation could be improved by pursuing the British plan.

But there was one part of it that once again encouraged Europe to take a hard attitude to talks: the threat. May's pledge to turn Britain into an offshore tax haven if Europe did not play ball was almost as damaging as the Rudd speech. It created the impression Europe was now in a fight for its livelihood. It suggested Britain was an opponent rather than a future partner.

If Britain could follow through, this approach would have been merely unpleasant. But it cannot, so it was also stupid. The rhetoric is not backed up by strength. Britain was behaving like the drunk man in a bar starting a fight with a much bigger guy.

The advantages Britain did have, like the timing of Article 50, it threw away for short-lived praise from the tabloid press. The disadvantages, like the lack of trained trade negotiators or the punishing Article 50 timetable, it did little to address. Instead, it entered into a period of sustained mania in which senior figures, including the foreign secretary, claimed it would be fine for Britain to fall onto WTO rules. David Davis kept insisting it would be worse for Europe than the UK, which makes zero sense given the relative size of the economies and their trade with one another.

So it was encouraging that Hammond today said there was "no doubt" the UK would be fighting hard for a deal. It was encouraging he did not publicly say today would be a cut off point for new EU migrants, as hard Brexiters had encouraged the government to do.

A new sense of realism, moderation and productiveness seems to be slowly overtaking the government, reflecting the reality of negotiations in which it is at a structural disadvantage. That's welcome, but it comes far too late. This attitude should have been in place since the start, when we realised what we were facing. Instead, ministers have paid more attention to their domestic political concerns than how that might translate across the Channel. Their approach will have made negotiations more difficult and a positive outcome less likely.

The phoney war is over. It showed Britain at its worst: fuelled by emotion, inward-looking and stuffed to the brim with a hysterical form of entitlement. We can only hope that the change of approach is sustained and that it neutralises at least some of the damage that we have done. Given ministers' track record, there is little reason to be optimistic.

It is likely that today will be looked back on as a mistake of historic proportions, not just because of the goal it seeks to achieve but because of the foolishness with which it has been pursued.

Ian Dunt is the editor of Politics.co.uk. His book - Brexit: What The Hell Happens Now? - is available now from Canbury Press.

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.