The competition to say the stupidest thing about Brexit has been won by Nadhim Zahawi

Of the many inane things uttered during the referendum campaign and its aftermath possibly the most fatuous came from the mouth of Conservative MP Nadhim Zahawi last Thursday morning on Radio 4.

“You don’t have to have a trade-off,” Mr Zahawi insisted several times, when John Humphrys of the Today programme pressed him about the future of Britain’s economic relations with the rest of the European Union. Actually the opposite is true. In this world, one almost always has to have a trade-off.

But what is a trade-off? So grievously misled and woefully under-informed have ordinary people been left by politicians and large sections of the media in recent months that it’s worth spelling it out.

To put it simply, in life you cannot have everything. There are sometimes two or more desirable things that you want but which you cannot enjoy simultaneously. Having one thing means you cannot have the other. Or it means having more of one thing means you must have less of the other. In choosing, you have to “trade off” different benefits.

To put the point in terms even an obtuse Conservative MP might understand, the party can elect a new leader with Theresa May’s track record of administrative competence or it can elect a leader with Michael Gove’s iconoclastic zeal. But the party cannot do both. These are two different people and there is only one position of leader. There has to be a choice made by MPs; there must be a trade-off.

This logic dominates decision making in families, in economics, in politics, in international relations – indeed, in just about every element of our individual and collective lives.

There are, it is true, sometimes “win-win” scenarios out there. Loving one of your two children does not mean you have to love the other any less, for instance. But these examples are vanishingly rare. In most areas of life, we do have to choose.

And the trade-off logic certainly applies in relation to the most important question of the moment: Britain’s future relations with the rest of the EU.

It might be possible for Britain to retain access to the European Union’s single market for goods and services without being a full part of the bloc. Norway has this arrangement. That’s certainly a very important benefit as far as the UK’s exporters are concerned. And it’s something many pro-Brexit Tory politicians appear to want.

But there’s another benefit these politicians desire: a liberation from the European Union rules which give people the right to work in any of the countries of the bloc. While the UK might secure a Norway-style arrangement, European politicians have made it very clear they will not agree to this while also permitting the UK to opt out of free movement of people. Norway is required to allow free movement as the price of its single market access.

The reasons are obvious. Britain is not the only country where there is popular opposition to immigration. If the UK is allowed to retain the manifold benefits of the single market while also pulling up the drawbridge in the face of EU migration, many of the other 27 member states would surely demand similar deals. Eventually the single market – which is built on the foundation of free movement – would collapse.

So, in the real world, the Brexiteers’ two desires have to be traded off: freedom of movement versus the single market.

And, in truth, this was always the trade-off that would need to be faced in the event of a Brexit vote. The scandal of the referendum campaign is that Leave politicians never admitted it, or discussed how they would approach it. They encouraged the public to believe that in voting to leave their livelihoods would not suffer (thanks largely to retaining single market access) but that Britain would also be able to drastically reduce immigration.

It’s not just anti-immigration Brexiteers who refuse to recognise trade-offs. Trade unionists often demand that governments make it much harder for firms to shed workers, failing to acknowledge that this can have the side effect of curbing overall employment. Environmentalists lobby against new housing developments that might harm local wildlife, failing to acknowledge that putting a brake on construction means fewer homes for young families in the area.

That a particular course of action has a negative side effect does not make it wrong. But there is a depressing tendency to deny that those negative impacts exist – or to seek to blame them on other outside forces, such as the wickedness of employers, or greedy outsiders hogging scarce local housing.

Speaking of which, how long will it be before the economic pain of Brexit is cynically attributed to the vindictiveness of the rest of Europe and its refusal to give the UK everything it demands?

“My policy on cake is pro having it and pro eating it.” That line can be found in a book titled The Wit and Wisdom of Boris Johnson. Yet, as we’ve seen, there’s no wisdom in there. And the joke’s really not funny anymore, as Britain is left to navigate an agonising trade-off that he and others denied.

Conviction politicians are often admired. We tend to think it’s a good thing when people have strong principles and stick to their guns, even when we disagree with them. Yet conviction needs to be married to honesty and openness to be admirable.

When politicians deny the existence of trade-offs they are not only deluded – they are dangerous.