Unlike Government these boards have their plans in place, so the decision is simply to activate them.
The exodus will then begin in earnest next spring, and once started will be difficult, if not impossible, to reverse. These things acquire a momentum of their own.
Interestingly, according to Rolet, the London Stock Exchange is itself among those which might have to move some of its operations, particularly the sophisticated clearing of interest-rate swaps and other derivatives.
At present these operate under a joint US/UK regulatory framework which in effect allows the Stock Exchange to operate under a US regulatory licence, something not copied anywhere else in the EU.
If these clearing operations have to move, it would be to New York, not anywhere on the Continent.
More generally, Rolet said that if the City’s expertise becomes fragmented it will move to Asia, especially China.
This does not spell the end of the City but you have to be a peculiar kind of masochist to believe as some do that it will make it stronger.
Rolet’s second point was that, in or out, the UK’s future depends in large part on having a thriving small and medium-sized enterprise sector which has access to the capital it needs for growth.
To have any chance of achieving this the country needs a long-term capital plan which plays to the strengths of all the different forms of finance, so these can be mobilised to support businesses.
Partly this is about organisation as well as money — it means proper well-resourced aid for exporters and requires much better partnerships between universities and business.
But crucially it really means Government has to support long-term patient capital and make business less dependent on debt.
The system needs to be changed so that the small business no longer feels that the best way to grow is by selling out.
The alternative has to be that it can raise capital directly from investors, because only equity looks to the upside — only equity allows businesses to think and plan for the long-term.
There is, he said, a £7 billion subsidy for debt across Europe whereas equity is taxed four times in its life cycle, so the tax system has to change.
At the very least it should no longer be possible to set interest payments off against tax, so the system is no longer so biased in favour of debt.
If the Government gets behind the capital markets in the right way then business can be transformed in the way the United States was transformed in the Nineties, he says.
Citing that precedent, Rolet reminded his audience that Japan appeared to be all-powerful in the Eighties and was grabbing an ever-increasing share of the markets where the US had dominated.
But the US response was to change fundamentally how capital was deployed with the arrival of high-yield bonds and other capital market instruments.
This resulted in more sophisticated capital allocation so that companies had to innovate and invest or be taken over and broken up.
Thus US business was transformed with the mass transfer of resources to technology and the rapid decline of traditional businesses where it could no longer compete.
Today there are four times as many SMEs in the US as there are in the EU.
The UK needs a nationwide programme to create more innovative SMEs.
It should be the national priority.
But it is a sign of the bizarre world of politics that such an agenda is heard more often in the Labour side of the political divide than from a Conservative party which can think of nothing but Europe.