I once asked Rupert Murdoch why he was so opposed to the European Union. “That’s easy,” he replied. “When I go into Downing Street they do what I say; when I go to Brussels they take no notice.”

That was some years ago but things have not changed that much. Size matters. Individual countries buckle but the EU is big enough to resist. British politicians have to fawn to foreign businessmen so they will invest here. The much-maligned bureaucrats in Brussels can afford to be much tougher — as Honeywell, Microsoft and Murdoch have found in the past and as Google is finding now. That, indeed, is one of the few real certainties in an EU debate which is largely fact-free.

Likewise with governments. Matthew Elliott, of Business for Britain, and in the Brexit camp, says we would be free to negotiate our own trade deals with the rest of the world. He should heed the words of a leading American trade negotiator discussing the slow progress being made on a trade deal between the US and the EU. It was taking time, he said, because the US was having to learn how to deal with an adversary who was an equal. This was in stark contrast with the way the US deals with individual countries. “Normally we just fax them our terms and tell them to sign.”

Yesterday Elliott also told a conference organised by EEF, the manufacturers’ organisation, that Canada had just done a deal with the EU which abolished 98 per cent of the tariffs of manufactured goods. He failed to mention that the pact took seven years to negotiate and failed to cover services, which are what we export most. Indeed, he failed to mention that trade pacts rarely cover services at all because they are too contentious. After listening to him, the audience — of manufacturers — voted 82 per cent to 13 per cent to stay in.

As anyone trying to follow the EU debate will by now have realised, there are almost no undisputed or undisputable facts to support either side. Brexit is actually a battle of ideas — it is about what people want to believe, not about what is provable. We are talking about two contrasting visions of the future. We also make a big mistake in looking to economists for answers because they do not deal in facts either. Theirs is an art not a science; the currency of economics is interpretation and opinion.

Of course they can produce facts about how well we have done in the EU but what they cannot do is prove that we would not have done equally as well outside. Thus 30 years ago a large number of coastal towns in the UK still pumped raw sewage into the sea and polluted the beaches. It was Brussels regulation which forced a clean-up.

Thirty years ago airlines in Europe were almost all state-owned and charged massively high fares. It was the EU which broke open the cartel and gave birth to easyJet, Ryanair and low-cost air travel. Thirty years ago there was no requirement to allow disabled access to buildings and transport; it is EU regulation which forced the changes to these too.

Currently there is a debate about the appalling air quality in central London. But the regulations which we so lamentably fail to comply with were developed in the EU not the UK.

But the Brexit camp will argue that we might have got there on our own and all these things might have happened anyway. There is no answer to that. The grass may be greener on the outside, as they say, but there is no evidence to support this because the only other country which has ever left is Greenland, with a population of 50,000 people and a concern only with fish.

That is ultimately why it pays to study behaviour, because what people and organisations do gives us a clue as to what is likely to happen. If Japanese car companies built plants here because we were inside the EU, are they more likely to expand them or contract them if we leave? Would the Chinese, who are currently deliberately destroying Europe’s steel industry by dumping huge volumes of the stuff below cost, decide in future to do a special deal with a generous exemption to Britain?

If American drug companies are already trying to break the power of the National Health Service so that they can charge more for their products, will they step up or reduce the pressure with Britain on its own?

Likewise the City. Why would an American, Jamie Dimon, the head of one of the world’s largest banks, J P Morgan, say Brexit would cause “massive dislocation” in the City if it were not true? American and Swiss banks have huge businesses here because it gives them access to the whole of Europe. Will they stay if that access is denied? Even if they do stay, will their best people want to work outside the mainstream? The collapse of sterling this week suggests some have doubts.

We do not know in economics what will happen next week or next month; and what will happen in the event of leaving the EU cannot be predicted so there is no point in seeking certainty.

There is, however, one fact cited yesterday by the pro-EU MP Damien Green at that same EEF conference. He said his father fought in a war in Europe where millions died; he was brought up in a Europe divided by the Iron Curtain; his children go for weekends in Poznan or Prague as routinely as they go to Preston or Peterborough. The fact is that the EU has made Europe an infinitely better place. To put that in jeopardy by leaving is to play a dangerous game.

But Brexit is not about facts, it is about feelings and emotion. Brexit is not about economics, it is about the kind of country people think they want to live in and the kind of people they think they are. It is not a factual matter, it is like faith: you believe or you don’t — and that’s why the outcome is so uncertain.