The results were pretty frightening. The social researcher picked up the phone and, using the most commanding tone he was capable of, announced himself to be a doctor. The nurse who answered the phone was given an instruction - go and give a certain dosage of a particular drug to a named patient.

They did. One nurse after another. A full 95 per cent of those who were called went to the medicine cupboard, collected the drug and set off towards the patient's bed. This despite the fact that the researcher wasn't actually a doctor or anyone known to the nurse, that the drug wasn't cleared for use and that the “prescribed” dose was dangerously excessive.

The authority of office is a pretty strong convincer. It doesn't even need to be real office. Dress up in a uniform and you can get perfect strangers to pick up litter in the street for you. The Labour Party used to get a man called Leonard Fenton to speak for it on NHS policy because he played Dr Legg in EastEnders.

And this, as I'll explain, is one of the reasons - just one - that I am not convinced that the conventional wisdom is right. I am not sure that an economic downturn is all bad news for Gordon Brown. At least not politically. I actually think it might help him.

The first cause to doubt the conventional wisom can be found in the headlines themselves. “World Markets Plunge”. Over the past quarter of a century voters have gradually come to understand that governments do not determine the state of the economy by themselves. They realise, to some extent at least, that powerful forces are at play, out of the control of politicians.

In times of prosperity this can be frustrating for politicians. I recall focus group research informing ministers in John Major's Government that voters hated him attempting to take credit for prosperity. We developed careful phrases to try to get round the problem. I smile when I hear Gordon Brown praising his own policies and then hastily name-checking the British people for their hard work. That was one of our formulas too. And much good it did us.

However, when the economy is doing less well, this all works out rather differently. The understanding that global forces are at work helps the government rather than hinders it. The refusal to credit politicians turns into a reluctance to blame them. Most polls seem to suggest that voters will not regard this Government as responsible for the downturn.

A global downturn also brings into a play one of the strongest forces in human affairs - risk aversion. A fashionable area of economic research is the exploration of the way that people make decisions under uncertainty. Repeated experiments demonstrate our reluctance to accept a bargain with an uncertain payoff rather than another bargain with a more certain, but possibly lower, expected payoff. When faced with a choice between the devil they know - Gordon Brown - and the devil they don't - David Cameron - voters may prefer to stick with Mr Brown.

Part of this research, employing experiments with gambling and such like, shows the much greater impact of losses on human beings, and the prospect of losses compared with gains. In an ordinary election two parties might fight over which has the best offer, which provides the bigger gain. The risk involved in making the wrong choice - sacrificing a gain you haven't yet made - doesn't loom all that large. Losses, according to many of these new school economists, are a different matter. If you make a mistake and lose more than you bargained that you would, it is much more painful. Voters in elections where economic losses are in prospect are likely to be more risk averse.

This is where the authority of office comes into it. Mr Brown is able to rely on his cloak of office and his title as surely as those fake doctors on the telephone. Flying off to world summits, calling sombre meetings of the Cabinet, making speeches in Davos or wherever about the World Trade Organisation, Mr Brown can use the downturn to strengthen his authority, and his authority to help him to deal with the downturn. Over the next two years it may be difficult being Prime Minister, but it will still be preferable to being Leader of the Opposition. For the Prime Minister can use his authority to make himself appear by far the less risky option.

And this will have its own impact on the Tories. Mr Cameron may be tempted into pessimistic rhetoric, abandoning his more successful sunshine strategy. Some in his team may feel the downturn justifies him employing tougher rhetoric, stepping up the attack on the Government, making the Conservatives once more look harsh, and making Mr Cameron look less prime ministerial.

There will also be a temptation to produce a more radical policy programme: desperate times, after all, call for desperate measures. There is already pressure on the Shadow Chancellor, George Osborne, not to repeat his commitment to match Labour's spending totals. This sort of pressure will intensify. And if the Tories give in to it, they will then be making themselves appear as an even bigger risk.

There has been a great deal of comment about John Major and Black Wednesday. Perhaps this will prove to be justified. The Government is certainly in a mess. But there is another Major parallel worth remembering too. In 1992 the fear of a further downturn helped the Tories back into office.

daniel.finkelstein@thetimes.co.uk

Times Recommends

• Copenhagen will fail – and quite right too
• They’re still wriggling to avoid the flak on Iraq
• Rule the waves? Not any more we don’t