The latest instalment of our series, in which we use the Centre for Cities’ data tools to crunch some of the numbers on Britain’s cities.

The reasons why a slim majority of the British people voted for Brexit back in June 2016 are many and varied. But one of them, I think, was a vague sense that the British economy was somehow being held back through its links to Europe – that we were, in the charmingly offensive phrase of Daniel Hannan MEP, “shacked to a corpse”.

This argument was nonsense on several levels: the Eurozone economy is now outperforming the British one; severing links with our largest trading partners is highly unlikely to put rocket boosters under the national economy. But there’s a bigger, more fundamental reason I’m not buying it: compared to those of most European countries, the British economy really isn’t that great.

To demonstrate this, we have to look beyond national averages, and drill down into the performance of individual cities. Below is a chart showing productivity rates in the capitals of the five largest western European countries: basically, how much wealth the average worker generates in a year.

(Some technical stuff, for those who wish to know. The data comes from the Centre for Cities’ Competing With the Continent database, which collated it from a variety of sources. The measure used is Gross Value Add (GVA) per worker, adjusted for purchasing power parities and expressed in pound sterling. The data is from 2011. More on methodology here if you need it.)

Anyway, here’s the chart:

There are no huge surprises here, I’d guess. Parisians are a fair bit more productive than Londoners, Romans a little less, Madrileños a chunk less than that. Germany may be the biggest economy in the EU, but its capital – surrounded as it is by what was East Germany – still cheerfully describes itself as, “Poor but sexy”.

Here’s the thing, though: capitals are not always representative of the countries they sit in. And London is by far the richest major British city. So what happens if we compare these five countries’ secondary cities?

First, we need to define our cities. For the purposes of keeping the data manageable here, I’m restricting myself to the five biggest European countries (Britain, France, Germany, Italy, Spain). I’m also only looking at urban areas whose populations Demographia puts at higher than 1m.

This presents us with a very slight problem: Demographia and the Centre for Cities define cities differently, and some of the “urban areas” listed by the former are counted as two or more different cities by the latter. Where that’s happened, in the name of simplicity, I’ve replaced the urban area with its dominant part: so Leeds instead of West Yorkshire, Birmingham instead of the West Midlands, Dortmund instead of the Ruhr.

That gives us a list of 19 cities to play with. Here they are with the population of their urban areas:

Dortmund (Ruhr), Germany – 6,670,000

Milan, Italy – 5,280,000

Barcelona, Spain – 4,790,000

Naples, Italy – 3,700,000

Manchester, UK – 2,685,000

Birmingham (West Midlands), UK – 2,550,000

Cologne (inc. Bonn etc.), Germany – 2,165,000

Hamburg, Germany – 2,105,000

Munich, Germany – 2,025,000

Leeds (West Yorkshire), UK – 1,955,000

Frankfurt, Germany – 1,950,000

Lyon, France – 1,650,000

Marseille, France – 1,620,000

Valencia, Spain – 1,585,000

Turin, Italy – 1,530,000

Stuttgart, Germany – 1,395,000

Glasgow, UK – 1,235,000

Sevilla, Spain – 1,110,000

Lille, France – 1,065,000

Here’s the same data as used in the chart above – GVA per worker, and so forth – for these 19 secondary cities. Once again, I’ve sorted them by size, and coloured the bars by country. See if you can spot any patterns.

You see the problem? The secondary British cities are much less productive than their continental peers, ranking lower than every other city in the chart except Naples. For all the talk of lazy southern Europeans that accompanied the Eurozone crisis, the cities of Mediterranean Europe are performing significantly better than those of northern England or western Scotland.

And the four British conurbations listed here contain just over 8m people between them, not many fewer than London. But where the capital is holding its own compared to its peers, the other big British cities are falling way, way behind. Even if London’s economy gives Britain an advantage, which is by no means certain, than it’s erased by the weak performance elsewhere.

Why this might be happening is an interesting and complex question, and in days to come I’m going to be trawling the data to find out. What is already clear, though, is that the gap on show here must shoulder a hefty blame for the state of the British economy. The problem is not that Manchester, Birmingham or Glasgow are not as productive as London: it’s that they’re not as productive as Marseille, Barcelona or Cologne.

I’ll be coming back to this topic shortly. But in the mean time, why not have a play with the Centre for Cities “Competing with the Continent” database?

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason.

Want more of this stuff? Follow CityMetric on Twitter or Facebook.