The mayor of Thessaloniki, Yiannis Boutaris, sighed. “Why are you doing this?” he asked. He was referring to Brexit. There were several aspects of it he didn’t understand. Why allow a simple (and small) majority vote to bring about such a massive change? Didn’t we understand the harm we would be doing to ourselves? He was forced to consider, sadly, that perhaps General de Gaulle had been right about us all along.

It is the fate of Brits abroad these days to get asked these questions. I was in Thessaloniki a few days ago to witness the launch of the new Empress Theophano prize, which will be awarded every year to people or organisations that have made an important contribution to European culture and identity, and that in particular reflect the rich diversity of Europe – its eastern (Byzantine) traditions as well as its western ones. Hence the involvement of many senior Greek figures, and the launch in this most historic city, where the Theophano Foundation, named after a 10th-century Byzantine and Holy Roman empress, is headquartered.

Civic and national pride was being displayed under a blue flag with a familiar pattern of gold stars on it

The governor of Central Macedonia, Apostolos Tzitzikostas, also spoke at the launch. He too embraced the symbolism of this prize and the occasion. “This is the right moment for us to leave aside introversion and look outwards,” he said. The importance for Greece of greater engagement in the European project and in the wider European economy could not be overstated. We need “more and better Europe, not less Europe”, he said. He wanted to help strengthen a common European identity.

But hang on a minute. This was Greece, wasn’t it? Poor, wronged, abused Greece, crushed by the heartless, savage neoliberals in Brussels? Surely “more Europe” would be the last thing they might be asking for after years of savage, EU-dictated austerity? On the contrary: the civic and national pride on display that morning were unmistakable. But this pride was being displayed under a blue flag with a familiar pattern of gold stars on it.

This ethos was further represented by the main speaker at the event, Herman Van Rompuy, the former president of the European Council (and predecessor to Donald Tusk). Van Rompuy is chair of the Theophano Foundation’s advisory council, whose members also include Sir Ivan Rogers, the UK’s former ambassador to the EU. Van Rompuy spoke forcefully of the need for greater European integration between west and east, and described the European Union as “the greatest peace project ever”. Nobody in the room demurred.

Later that evening I had the chance to have a conversation with Van Rompuy. It was a brief but intensive tutorial in European politics, and on what he felt Britain had got wrong in its relations with the EU. He began by reminding me that Greece’s economy had shrunk by around 25% after their crisis. “They had more reason to be angry than most,” he said. The UK, he observed, had joined the then EEC one generation after the founders. It had been the least integrated member state but even that was too much for some, he said. Even though Britain had been part of the peace process through its role in the second world war, it had not joined the EEC in search of peace, as other member states had done.

What Van Rompuy fears, on our behalf, is how hard the realities of isolation will hit. The fraught discussions over the withdrawal agreement have been merely the first sign of this. “You need allies and friends to have an influence,” he said. “When you don’t, you really have a problem.”

Some of this isolation can be traced back to David Cameron’s decision to take Conservative MEPs out of the EPP centre-right grouping. The UK government had no partners, no influence. (This view is shared by Daniel Caspary, head of Germany’s Christian Democratic Union MEPs, who recently told Politico: “Had David Cameron continued to attend the EPP’s pre-summit meetings, he’d have never have called that referendum.”)

Van Rompuy was also struck by Cameron’s choice of language. He had referred to the EU as an “organisation”. “But the EU is an institution,” Van Rompuy told me. “It is much more than an organisation.” The Brits had talked about “reforming the EU”. “You can have reforms in the EU, but that’s not the same as ‘reforming the EU’,” he explained. “After 40 years of marriage, Britain really didn’t understand the EU,” he said, sadly. “It’s unbelievable.” And as for getting any changes to the text of the withdrawal agreement, the chances are, Van Rompuy said, “Nil.” And he repeated for emphasis, “Nil!”, making a zero shape with his thumb and forefinger.

I hadn’t anticipated it, but heading east to the land of the ancients had helped provide some enlightenment about today’s problems. Isolation looks like a bad option, according to those who have felt most threatened by it. The Greeks are holding fast to the EU in spite of everything. It turns out the mayor of Thessaloniki asked a good question. Why are we doing this?

• Stefan Stern is co-author of Myths of Management and the former director of the High Pay Centre