At 9.30am, a week ago last Friday, there was a curious spectacle in Camden Square in north London. A great elbowing melee of the British media, in a crowd eight or nine deep, perching on garden walls, tripping over kerbs, was employing boom microphones and close-up lenses to capture the every word and gesture of a politician inching along the pavement. The curiosity lay in this fact: the politician in question was a Belgian member of the European parliament. Never in the 60-year history of that most-ignored institution can the national press pack have given such frenzied attention to canvassing by a foreign MEP. Brexit trails unexpected consequences.

The politician at the centre of the scrum was Guy Verhofstadt, the 66-year-old leader of the liberal group in the parliament, and its nominated representative in the Brexit negotiations. Verhofstadt is one of that mop-topped quartet of EU politicians – along with Jean-Claude Juncker and Donald Tusk and Michel Barnier – who have offered a mostly bemused chorus as the UK, centre stage, has proved serially incapable of not shooting itself in the foot. Individually, they have each acted at different times as targets for all the self-inflicted humiliation of that failure.

The focus on Verhofstadt on this particular morning lay in the fact that for the previous two nights, for those committed enough to forego watching the stirring European football semi-finals, the inside view from that “other side” of our government’s lamentable negotiations had been exposed for all the world to see.

At the beginning of the Brexit talks Verhofstadt had agreed to a Belgian documentary crew making a fly-on-the-wall of his office’s role in Brexit. The film was contracted not to be broadcast until after 29 March, when the UK had already left the union. In the event, Lode Desmet’s revelatory two-part film Brexit: Behind Closed Doors had appeared, at least for those determined to seek it out on BBC Four, with “negotiations” ongoing.

The documentary chose some of the more dramatic moments over two years. How you see it depends on your point of view Guy Verhofstadt

Verhofstadt enjoyed many memorable moments in the film. Here he was emerging from a ludicrous exchange with the European Research Group’s Andrew Rosindell MP, mouthing “wanker”. Here he was toasting his steering committee with the first of many late-night bottles: “we will work better with wine!”. Here he was persuading David Davis to be his pit crew as he raced his classic Aston Martin at Silverstone. And here he was divulging that Olly Robbins, Britain’s chief Brexit negotiator, had at one point asked him in a whispered aside about the chances of securing Belgian citizenship when it was all over.

For any grown-up viewer it would have been a stretch to watch the whole documentary without forming the impression that Verhofstadt had huge regret about the decision Britain had made, and was exasperated in his efforts to find the most pain-free solution for all parties.

Facebook Twitter Pinterest EU president Jean-Claude Juncker jokes with Verhofstadt in Strasbourg. Photograph: Vincent Kessler/Reuters

That, of course, is not how the stormtroopers of the Brexit party, and those who get their news from a bloke in his underpants in a bedsit in Northampton or a troll factory in Nizhny Novgorod, saw it. Clipped excerpts had circulated on social media, portraying Verhofstadt as the enemy “foreigner” incarnate. The Sun, not wanting to be outflanked in its xenophobia, had opened its leader column the previous day with this assessment: “No more repugnant figure struts the corridors of Brussels than the curtain-haired slimeball Guy Verhofstadt. Try as they might, even the drunk Juncker or the peacock Barnier cannot match the Belgian’s detestable blabbermouthed arrogance. And his top aide plainly shares his superiority complex. ‘I’m most proud of you when you take on a Tory and win,’ coos Edel Rettman-Crosse sycophantically to her ageing boss [in the film]. ‘You should shoo the fuckers out.’”

The man from the Sun, and those from the Express and the Mail were among those at the front of the scrum in Camden questioning Verhofstadt about whether his appearance in Britain was not more “meddling” in our democracy. Verhofstadt is a tall man, who has something of the look of David Mellor, had Mellor retained a personal trainer. He explains patiently, standing alongside Sir Vince Cable, that he is here not in his capacity as Brexit negotiator but to launch his own Flemish Liberal party’s campaign for the forthcoming elections and to lend support to the Lib Dems’ “Bollocks to Brexit” message. “These are European elections, and we are Europeans,” he says.

“Did Olly Robbins really ask you for Belgian citizenship?” he is asked. Verhofstadt laughs. “He did, but it was a joke. Obviously! What has happened to your great British sense of humour? Please don’t say you have lost that.”

Verhofstadt’s own sense of humour, which expresses itself in an ever-present half-smile and muttered asides in Dutch or French or English, is tested as he tries to follow Cable in the staged knocking of a couple of doors around the square. He’s an old enough hand to know that there is not much mileage in this circus so he retreats as soon as possible to a minibus. I take a seat with him as he is driven to the next leg of his short tour, to meet pro-EU demonstrators near parliament, and ask him if he regrets the timing and the tone of the BBC programmes. “The documentary is a documentary. It chose some of the more dramatic moments over two years or so. How you see it depends on your point of view.”

He is here not to exacerbate those polarised opinions, but to report on them, he suggests. The plan is to make a short film for Belgian voters that will illustrate the dire consequences of “not standing up against nationalism and populism” that Britain now, tragically, represents. “It is not only in Britain this is happening. You see it in Netherlands, you see it in France, you see it with Salvini in Italy and the AfD in Germany,” he says. “The difference is that since Brexit these groups are no longer saying they want to destroy the EU. When Farage said, ‘Now you will see other countries follow Britain’, a ‘Grexit’ and a ‘Frexit’, he was completely wrong. It has gone the other way.” As a consequence there was only one place to make their film: “You really want to know what the nationalists have done? Come to Britain, come to London and see what is happening.”

At the beginning of that week I had been out to the European Parliament building to talk to Verhofstadt in his natural habitat. He and his staff, including the newly famous Rettman-Crosse, occupy a corridor of rooms. On the wall at one end is a large vintage poster of David Owen and David Steel in the heyday of the SDP-Liberal alliance. Steel in particular was a friend and mentor to Verhofstadt when he was setting out on his own mission to argue for an unapologetic centrism in European politics.

The Belgian is, against all tabloid stereotypes, a fierce anglophile. One of the great loves of his life is his 1954 Aston Martin and everything that it represents. This love has rarely been reciprocated, however. Verhofstadt was among the most vocal opponents to Tony Blair’s failed attempts to secure EU backing for the invasion of Iraq in 2003. That refusal was not forgotten. Blair successfully vetoed Verhofstadt from becoming president of the European commission in 2005 – he was the favoured candidate of Gerhard Schröder of Germany and Jacques Chirac of France – on the grounds that he was “too much Brussels”. The shorthand encapsulates the British view of him up to the present. He would probably accept the description, without the implied pejorative. If you were to look for an embodiment of European unity it would be hard to ignore the claims of Verhofstadt. He is not only the most vocal advocate of a federal continent, with tax-raising powers and a shared foreign policy, he was born in the year that greater political union was first proposed, 1953.

Facebook Twitter Pinterest Verhofstadt races his Aston Martin in the Silverstone Classic, 2017. Photograph: Alamy

He is, like most European politicians of his vintage, a product of the determined utopianism of those postwar years. Not only was he born with the European Union, he was born to it. His parents had emerged from years of German occupation determined to ensure nationalist horrors would never again be visited upon the continent. His father worked, when Verhofstadt was a boy, as the legal officer of a liberal trade union. His mother – who is still going strong at 94 – was active in local liberal politics. “She was really the force behind me,” he says. “From as early as I can remember we spoke about politics all the time at home. We spoke about the Vietnam war, about the murders of Martin Luther King and John Kennedy…”

Verhofstadt was a prodigy as a politician. He was leader of his party at 29, deputy prime minister and minister of finance at 32; and then subsequently, having formed his own new Liberal movement, prime minister for nine years.

“I went from being president of the youth movement to directly being president of the party,” he says. “Completely crazy. I had already written two manifestos by the time I was 28 years old.” Both argued that liberalism needed to be a proactive not an apologetic force, taking on narrow bigotries wherever they were found.

When Verhofstadt became finance minister in a coalition government at 32, Belgium had the biggest deficit – 136% – of all the members of the EU. He gained a reputation as a fierce cost-cutter. “I went in there like un sauvage. I still say you don’t need to know mathematics to be the finance minister. You just need to be able to say the word ‘no’.”

Verhofstadt said that word for three years and earned the nickname “baby Thatcher”.

How did he feel about that?

“It didn’t bother me. I had some libertarian opinions at that time. I believed a lot in this more aggressive liberalism. In free markets and so on and it worked in a certain way. But then I went in opposition for 12 years and I created a new party...”

Rwanda transcended everything. When I looked back, in my previous period, I found myself to have been an asshole

The great change in his thinking at that time, he says, came when he visited Rwanda in 1994 to make a report for the Belgian parliament about the origins of the genocide in its former colony. “800,000 people had been slaughtered in the most brutal way in two months. UN troops had been there, Belgian troops had been there and it had happened anyway. I went into churches two years after the genocide, and the bones of the dead were still just piled high everywhere. That fact changed my politics.”

In what way?

“What happened there, the extreme of nationalism and religious tribalism, was of such a magnitude and such a cruelty that it transcended everything. Some people might say I became a little more liberal about human values and a little less concentrated on fiscal questions as a result,” he says. “For me when I looked back, in my previous period, I found myself to have been an asshole.”

His new movement had above all to be clear about what it was fighting against, he suggested. Liberalism had to be emotional as well as pragmatic. “I won the next election, because I was speaking more from the heart,” he says. “I became prime minister, and I did in total nine years.”

Facebook Twitter Pinterest With Tony Blair in 2000. He strongly opposed Blair’s attempts to secure EU backing for the invasion of Iraq in 2003. Photograph: Johan Martens/EPA/Rex/Shutterstock

He has carried those beliefs into his career in the European parliament, where he tried not to ignore the opponents of closer union, but to take them on. Most MEPs have looked on tight-lipped as Nigel Farage has pitched up to make his setpiece speeches, designed to be amplified on YouTube channels and Russia Today, and hoped he would eventually go away. Verhofstadt, over a decade, is the one politician who has consistently tried to challenge him toe to toe. Farage routinely describes the Belgian as a “zealot” and an “extremist”. Verhofstadt in turn mocks Farage’s dismal attendance in the parliament, suggesting the greatest waste in the European budget had always been the British MEP’s six-figure salary and lavish expenses.

He agrees that Farage’s power is that he is able to say exactly what he thinks, and to say the same for every audience; that is a rare commodity among European politicians, who find themselves saying one thing to domestic electorates and another to European colleagues. You challenge that, he insists, by being open about the failings of European democracy, not defensive.

“I am criticising the European Union more than the Eurosceptics,” he says. “But on the recipes to improve it we differ completely. They want to go back to the past, to put up all the old borders, and the so-called sovereignty of the nation states…”

So-called sovereignty? I ask. “We all know national sovereignty is meaningless when you talk about climate change or migration or security. You can only gain sovereignty over those issues by using the added value of a common approach. The only way to react to Trump’s protectionism, for example, is to have the collective power to take counter-action.”

He makes this argument, he insists, not because he favours centralised power – far from it – but because federalism is the opposite of centralism. “It is only the British who do not really understand that,” he says. Every other European nation acknowledges that on the federal level you do those overarching things collectively, “then clearly some things are best organised at the state level, and most things at the local level”.

In some ways of course, his own nation, as Nigel Farage never ceases to point out, is the most fragile example of such a collective will…

“It is fragile, but it works,” he says. “We speak different languages, but Belgium is a country that has existed since 1830. It is older than Italy and Germany.”

Verhofstadt called his latest book, published after the referendum result and the migration crisis, Europe’s Last Chance; it sets out his fears that without a unity of purpose the continent will fall behind in the new world order. “With China rising as a civilisation; India, with its 2,000 nations, 20 different languages, four different religions but one single democracy; the US where Spanish will be spoken as widely as English in a few years; the Russian federation and all its issues on our border… In such a world there is only a future for Europe: together. And you will not be successful in that if you have a budget of 1%. Compared to the American federal budget of 25%…”

It is almost impossible to imagine his vision of a federal Europe, with greater tax-raising powers, being realised if Britain were a part of it. In that sense does part of him welcome the imminent departure of the most intransigent cherry-picker of EU rules?

“No. I have always said if you cannot keep inside your union a great country like the UK then you have failed. Brexit makes the reform of the union more urgent. We should be inspired by Churchill, a great lover of the best things of Europe – the champagne and all the rest.”

Facebook Twitter Pinterest Guy Verhofstadt: ‘When, if ever, will they put country before party?’ Photograph: Antonio Olmos/The Observer

He tries his hardest to keep up that latter Churchillian commitment; his life is a kind of manifesto for European culture. He met his wife, Dominique Verkinderen, a celebrated soprano, at 17, 48 years ago; at the height of her career in baroque and pre-Romantic music, she was performing 60 concerts a year all around the continent. They have two children, now grown up. As well as a home in Brussels they have renovated a house on a hill in the centre of Italy on the border between Tuscany and Umbria, where Verhofstadt has developed a hobby vineyard. “I believe wine is civilisation,” he says. “It is easy to say I make wine but it is very difficult to do it well.”

He spends as much time travelling the continent as he can. Besides the event in London, his campaigning for these elections is planned to take him to Dublin, Bucharest, Madrid, Budapest. (The day after he met the Lib Dems he was due to be out with Emmanuel Macron’s “Renaissance” group in Strasbourg but was in hospital in Paris, having felt unwell).

On the bus in London, I asked him the obvious question of how he thought Brexit would go in the coming months, whether he felt he would ever escape from it. “Like you, all we can do is watch,” he says. “The withdrawal agreement is there. We are ready to sign it. My view is that in any other country, after such an existential decision as the referendum, there would have immediately been a cross-party commission. But you seem to prefer always the usual two-party fight. Like many of you, we are just asking, when, if ever, are they going to put country before party?” He believes this week’s elections are a good place to start.