THERE is a silly little lie that keeps getting told about Britain. The UK, it goes, is the sixth richest country in the world.

We have all heard this ubiquitous zombie fact as it lurches and stumbles through our politics.

For some commenters, it is a matter of pride. For others, it is a rhetorical device to highlight the horrors of poverty and inequality.

Few seem to care that it is not actually true.

Britain’s economy, at least in nominal terms, really is the planet’s sixth “biggest”, behind India, Germany, Japan, the United States and China, But the sixth “richest”? Nothing like it.

In fact, the UK currently ranks 22nd in the world in Gross Domestic Product per capita, when the total output of the state is divided by how many citizens it has. Adjusted for real price comparisons, we fall even further, to 29th.

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This is not news – these are easily available public figures; they should not surprise anybody who has been paying attention.

And Britain’s position in the world league table of wealth is far from terrible. We come in just ahead of Israel and just behind South Korea – and the EU average, at least according to the most recent comparative data from the International Monetary Fund.

Hey, the “sixth richest nation in the world” line has been roundly debunked over and over again. But its resilience to fact-checking is still fascinating. I suspect this is because the “fact” speaks to one of the deep, unquestioned premises of our public discourse: that we live in a very wealthy state, even when so many of its citizens are quite obviously rather poor.

Sometimes what is most interesting in politics is what everybody assumes to be true, the unchallenged assumptions that inform every debate, every disagreement that we have, whether they, like a cheesy TV movie, they are “based on reality” or not.

But what if we are just not “all that rich” any more? How long is it going to take for our political patter to catch up with our real level of economic oomph?

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The good news is that Britain’s relative descent, at least until Brexit and Covid, has been slow. But that has just meant we, like boiling frogs, have not really noticed.

Yet, my goodness, things can really change over decades. To see how, let us take a simple comparison – just on crude unadjusted GDP per capita measures – with our nearest neighbours.

The World Bank has a wonderful interactive online tool that lets you compare the economic performances of states over time.

It has robust numbers for 1966. Back then the UK’s GDP, divided by every citizen, was nearly double that of the Republic of Ireland. Scroll forward to 2021 and this position has effectively reversed.

OK, to be fair, the contrast with Ireland is unusually stark. And GDP, of course, is not the be-all-and-end-all of anything.

But the UK lags behind its other neighbours too. Take Germany. It absorbed its poorer Communist East just 30 years ago and is not some land of milk and honey. As recently as before the financial crash its crude GDP per capita was behind Britain’s.

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The latest numbers on the World Bank’s interactive tool show Germany pulling well clear, by nearly $5000 per person.

These figures matters. Lots of little stories only make sense when you bear them in mind. There was a mini press stushie last month because authorities in Lanzarote – the Canadian island Brits love for its winter sun – were touting for “higher quality visitors” in Berlin.

Well, doh. Of course the Spanish would rather have better-off tourists.

The “Britain is very rich really” narrative has been laced through our politics for decades. It informed what passed for debate on Brexit, convincing many people that the EU needed us more than we needed them.

The myth featured strongly in 2014 indyref too. Unionists relied heavily on the perceived economic stability of the UK – its “broad shoulders”.

Nationalists – buoyed by what turned out to be short-lived spikes in oil prices – declared an independent Scotland would be one of the world’s richest nations.

It was as if all we had to do to get the keys to a secret treasure chest was to cast a vote for Yes.

Scotland’s real economic position, incidentally, is remarkably middling by both UK and EU standards.

Politicians like to compare our wet little country to sovereign states. But – at least until Brexit – we had some very helpful like-for-like comparisons with nations and regions of roughy our side, Eurostat’s NUTS 1 accounting units. As of 2017 we were just below average in the EU on Gross Value Added or GVA, a measure of regional rather than national economies. Can we hold that position? Hmmm.

Herald Business Editor Ian McConnell on these pages only yesterday was suggesting that the UK – like in the 1970s – was the “sick man of Europe”.

Mr McConnell – who over recent years has grimly catalogued the devastating effects of Brexit on Scotland – has a strong point: the British economy is underperforming key peers. Prices are rising across Europe, but just not as fast as in the UK.

There have been other multiple warnings of a return to the 1970s in the British press. Which is quite funny. Why? Because the UK economy fared better in that supposedly awful decade than now or indeed than under the zealous free market reforms of industry-wrecker Maggie Thatcher. We wish we had the growth we enjoyed half a century ago.

We are starting to see a bit of politics around Britain’s relative decline. Sir Keir Starmer – who remains wedded to Brexit – recently warned the UK, on current trends, would be overtaken by Poland by the end of the decade. The Labour leader, of course, does not have a crystal ball. But his patter is worth thinking about: why do we assume we will be better off than, say, Poles?