Doused in milkshake by a mob chanting 'Nazi-scum', a middle-aged man is led away by police for his own protection. His crime – to express words of welcome for the President of the USA.

This was the scene beneath the statue of Sir Winston Churchill in Parliament Square yesterday just a couple of hundred yards from the room where Donald Trump and the Prime Minister were holding talks on the second day of the President's state visit.

Outside, a smaller-than-expected 'Stop Trump' demonstration was not in the mood to hear dissenting voices. Moments earlier, the same man had been heard telling protesters that Mr Trump 'speaks the truth' about Brexit.

A Trump supporter had milkshake thrown at him by a baying mob in London yesterday

Oops. This did not go down well with a crowd who had just been wildly cheering Jeremy Corbyn as he accused Mr Trump of 'Islamophobia' for criticising the (Muslim) Mayor of London during Ramadan. There was similarly enthusiastic applause for Green Party MP Caroline Lucas as she attacked Britain for 'pimping the Royal Family' on Mr Trump's behalf. The Scottish Nationalists' Westminster leader, Ian Blackford, even accused Mr Trump of 'betraying' his Scottish ancestors with his policies on immigration.

Welcome to the dizzying heights of the moral high ground as this grand coalition of the righteous gathered yesterday to heap abuse on the leader of the free world.

In the event, however, it was all as underwhelming as the weather.

What had been grossly over-hyped as a 'carnival of resistance' turned out to be a rain-soaked exercise in adolescent raspberry-blowing.

A 16ft schoolboy Trump sat astride a lavatory at one end of Whitehall while an inflatable nappy-wearing Trump barely got off the ground at the other. In between these two satirical masterpieces, a crowd – which had been forecast to exceed 250,000 but barely mustered five figures – heard a succession of Left-wing activists repeat the usual charge sheet against Mr Trump.

A supporter of President Trump gets 'milkshaked' as fights break out at anti-Trump protests in central London

A pro-U.S. President Donald Trump supporter is pushed by anti-Trump demonstrators during a rally against Trump

Some threw in a few choice expletives to raise a cheer and show how, like, really angry they were.

Many expressed their outrage that Mr Trump should be on friendly terms with Brexiteering villains like Boris Johnson and Nigel Farage.

Brexit, it transpired, was the reason why many of this lot had turned up yesterday. The blue-and-yellow army of shouty Remainer ultras haven't had a good shriek outside Parliament for some months now. The presence of Brexit-loving Mr Trump was the perfect excuse for a reunion.

Shadow foreign secretary Emily Thornberry went as far as suggesting some sort of post-imperial intervention at the White House as she delivered a stern warning to Mr Trump: 'We are not going to allow you to be the representative of the United States that we believe in!' George III and his ministers tried something similar back in 1776, Emily, and that did not end well. But then there has always been something distinctly vice-regal about Lady Nugee (to give Miss Thornberry her correct title).

How infuriating for her and the rest of the anti-Trump coalition that everything inside the rocket-proof security cordon seemed to be going so well. Following on from Monday's spectacular events at Buckingham Palace, the bilateral glow remained undimmed yesterday. Even Theresa May appeared to be having a lovely time.

The man found himself in the middle of an angry mob yesterday afternoon at the rally

Here on the outside, however, the atmosphere was sour and spiteful. Those politicians, including the leaders of Labour, the Liberal Democrats and the SNP plus the Speaker of the Commons – who had made a point of snubbing our most powerful ally, have been left looking naive and unprofessional.

None could produce a coherent explanation for their willingness to embrace non-democratic state visitors, such as the President of China, while ostracising the elected President of the USA.

The irony was not lost on the handful of pro-Trump supporters who had decided to make a stand in Parliament Square yesterday. Earlier on, I encountered the man who was later covered in milkshake. He was part of a group waving the Stars and Stripes. Given that he was also wearing a 'Make America Great Again' Donald Trump baseball cap in the middle of a crowd like this, he and his group must have been expecting a reaction.

'Love him or hate him, he's our greatest ally and he's here to commemorate D-Day so we should show some respect towards him,' explained retired company director Lorraine Chapel, from west London. As she spoke, a group of EU flag-wavers, many in Liberal Democrat T-shirts, squared up to the group, calling them 'fascists'.

'F*** Trump. How dare you support him?' shouted one of the anti-Trumpers, a German academic called Daniella. 'Don't swear at me, please,' countered Lorraine. Police were soon on the scene to calm things down.

Nearby, the team in charge of the 'Baby Trump' balloon were keeping their toy tethered close to the ground. They had been granted two hours of flying time by Mr Trump's nemesis, the Mayor of London, Sadiq Khan, but their permit coincided with adverse weather. It was the same balloon which caused such a stink ahead of Mr Trump's visit to London last summer and had, thus, rather lost its novelty value.

Its owners had appealed for £30,000 ahead of yesterday's event, explaining that the money would be used to fund the overall costs of the demonstration.

Certainly, there can be few other countries where protesters would be allowed to voice their feelings so close to a visiting world leader. While Mr Trump was inside Downing Street, the demonstrators were only just outside the gates at the end of the road.

A stage had been erected next to the Cabinet Office on Whitehall. Having assembled in Trafalgar Square, next to Trump-on-the-toilet, the various pressure groups then marched the short distance to the stage, led by the Palestine Solidarity Campaign. They were followed by climate change groups while the 'Hands Off Cuba' brigade brought up the rear.

Last night the woman who screamed 'Nazi', Siobhan Prigent wrote on Twitter: 'I am very sorry for my behaviour today. I should have protested peacefully and I didn't, and I regret that. I've let myself down and I do understand that fully'

All told, the crowd was exactly the same size as the Royal British Legion parade which I have seen filling the same stretch of Whitehall every Remembrance Sunday for as long as I can remember.

Given that the Legion parade is always limited to 10,000 marchers, we can safely put yesterday's crowd in the same bracket.

Last night, however, organisers were gamely trying to claim a figure of '75,000'. On that point, Mr Trump was indeed entitled to shout 'fake news'.

The master of ceremonies, Guardian columnist Owen Jones, did his best to get everyone in the party mood with chants of 'Say it loud, say it clear – Donald Trump's not welcome here.' It was hard work. 'God, it's like panto,' sighed Jones at one point.

A succession of Leftie luminaries, poets and alleged comedians did their bit. Frances O'Grady, general secretary of the TUC, invoked an unlikely hero in the form of the Duchess of Sussex. Noting that Donald Trump had called the former Meghan Markle 'nasty' (the President insists that he was referring to some 'nasty' remarks, not Meghan herself) Miss O'Grady continued: 'Better to be a nasty woman than a dirty old man!'

That, more or less, set the tone. Calling Mr Trump 'a mortal threat to all of us', Mr Jones introduced a 'flow poet' whose opening stanza began: 'F*** racism, F*** Boris'. The shadow home secretary Diane Abbott – described by the organisers as 'the People's Auntie' – also attacked Mr Trump for being 'abusive' to the Mayor of London.

Another trade unionist, Mark Serwotka, president of the TUC, issued a call for increased migration to the UK and, by implication, attacked all those who had attended Monday night's banquet for Mr Trump at the Palace.

'What makes Jeremy Corbyn and Diane Abbott different is they won't break bread with a racist!' he declared to loud cheers.

Since Mr Corbyn has famously broken bread with the IRA, Hamas and the kleptocrats of Venezuela, among others, this was debatable. But not among this crowd, of course. Mr Trump is utterly deplorable and that is that.

Say otherwise and you can have a milkshake on your head.

Last night the woman who screamed 'Nazi' at the Trump supporter in London apologised for her actions. Siobhan Prigent wrote on Twitter: 'I am very sorry for my behaviour today. I should have protested peacefully and I didn't, and I regret that. I've let myself down and I do understand that fully.'