The reasons why 17.4 million British people trooped to the polling stations last summer and put their crosses in the leave box have been endlessly analysed, and often crudely carved in half – as if some Brexit supporters were angry about immigration and others fixated on questions of sovereignty, and that was pretty much that.

But 10 years after the French bank BNP Paribas heralded the coming financial crisis by suspending two hedge funds that had effectively proved worthless, it’s worth reprising a pretty basic point: among the furies that exploded on 23 June last year were lingering grievances about the financial crash of 2007-8. The years since the cashpoints almost ran out had seen simmering anger about the endless billions pumped into the big banks and the lack of any obvious reckoning – not to mention exasperation with politicians chained to the demands of high finance, and not nearly interested enough in the millions of people whose only acquaintance with the City lay in the mess it had made.

To the delight of Irish estate agents, tailors and wine merchants, more than a dozen banks will shift business to Dublin

Clearly, the vote for Brexit represented a kind of misdirected, flailing revenge. As big banks lined up with the UK’s largest corporations to warn the public that Brexit would be disastrous, the sense of an instantaneous backlash was obvious. Former City insider Nigel Farage well knew Brexit’s basic populist plotlines, and when he made his victory speech in the small hours of 24 June, he said that the leave campaign had knocked down three adversaries in particular: “multinationals”, “big politics”, and “merchant banks”.

Having got up off the floor, some of the City of London’s biggest players are now taking big decisions. They have contracts that extend way beyond 2019, but what Brexit negotiations might mean for them remains chronically unclear. Plans for their future European operations need to be made right now. So plenty of banks are starting to shift parts of their business outside London, to a surprisingly muted response. Philip Hammond, the chancellor, seems to know roughly what is at stake, but swaths of the Conservative party – that historic redoubt of traders, brokers and high-rollers – seem surprisingly unconcerned. After all, what have bankers – bankers – ever done for us? Part of the answer lies in the £70bn-ish of tax revenue paid by financial services in 2015/16 – about two-thirds of our annual spend on the NHS.

What is pushing banks away from London is obvious enough. In the wake of the referendum, there was a lot of talk about the City somehow retaining its “passporting” rights, which allow banks and fund managers to do business freely across Europe. Those hopes now look forlorn: indeed, the City’s biggest lobby group, TheCityUK, served notice that it was giving up the fight for such privileges back in January.

Given that Britain has said that it wants to leave the single market, the EU was hardly likely to allow the UK to retain one of that market’s lucrative elements, and the search for a possible substitute has now focused on so-called “equivalence”: arrangements for certain kinds of financial trading to continue, if the EU agrees that Britain’s regulations are in line with its own.

This may be all that the City has to cling to, but there are no end of drawbacks, not least the fact that such arrangements are unilaterally granted by Brussels, and can be revoked at a month’s notice. Small wonder, perhaps, that there is all that talk about possible transition periods. But even if we actually get to postpone the worst of Brexit, what happens in 2022, or 2025, or whenever we finally leave? And what of the big City interests who are already reshaping their operations?

Facebook Twitter Pinterest The French president, Emmanuel Macron. His people were ‘crystal-clear about their underlying objective: the degradation of the City of London’. Photograph: Etienne Laurent/EPA

To the audible delight of Irish estate agents, tailors and wine merchants, the authorities there say they have finalised deals with more than a dozen banks and finance houses for some of their business to be shifted from London to Dublin. JP Morgan – which warned during the referendum campaign that Brexit might mean losing a quarter of its 16,000 UK staff – has started building a 22-storey tower on the banks of the Liffey. Morgan Stanley is likely to shed jobs in London by expanding operations in Frankfurt; CitiGroup, Standard Chartered and Nomura Holdings are reportedly opening new offices in the same city. That much-loved public favourite the Royal Bank of Scotland apparently has its sights set on Amsterdam, which is nice.

So far the number of jobs involved seems modest but there will be more of these stories. When I called round a few City insiders this week and asked them how much of London’s financial business Brexit might cost, one put the figure at 25%. An LSE study reckons the potential loss of business revenue is around 15%; one Brussels-based thinktank says the value of assets about to be transferred to mainland Europe may total €1.8tn, equivalent to 17% of the UK’s banking assets. To state the blindingly obvious, in an economy as financialised as ours, that’s a lot.

Note also one particularly fascinating part of the story. Emmanuel Macron – either Europe’s great progressive hope or, depending on your view, a narcissistic schemer who fancies being the next Tony Blair – is a former investment banker. Back in the distant days when he was France’s finance and economy minister, he joked that he would “roll out the red carpet” for London-based bankers if Britain voted to leave Europe. He is evidently as good as his word: earlier this month, the City of London’s special Brexit envoy wrote in a memo that his recent meeting with high-ups at the French central bank was “the worst I have had anywhere in the EU”; and that Macron’s people were “crystal-clear about their underlying objective: the weakening of Britain, [and] the ongoing degradation of the City of London”.

Meanwhile, even bigger anxieties swirl around. Some relate to the disastrous possibilities of a cliff-edge Brexit, glimpsed this week in the letter written to the House of Commons Treasury select committee by the deputy governor of the Bank of England in charge of the Prudential Regulation Authority, which essentially exists to prevent financial crises.

He warned of threats to both the financial sector and the UK economy as a whole, as well as holding out a particularly chilling prospect: that just as personal debt reaches a critical point and warnings of financial fragility are once again heard, British regulators might be prevented from doing their usual work by the new responsibility of regulating the British operations of European companies hitherto overseen by other EU governments. He calls this a “material extra burden”; the rest of us might think of it in terms of accidents waiting to happen.

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This may be the first column I have ever written in defence of banks. If we had any kind of solid, dependable, balanced economy, we all might be much more relaxed. But there are no signs of that; indeed, leaving the EU looks likely to make the gaping inequalities the City symbolises even worse. The next time you are in a hospital or school, you might want to consider two things: that bankers foot a sizable share of the costs; and that, in the midst of Brexit’s mixture of anger, delusion and indifference, they may soon be paying their taxes somewhere else.

• John Harris is a Guardian columnist