On 6 January, or thereabouts, London will hit an extraordinary milestone. The population has finally caught up with its 1939 peak population: from now on, it will be an all-time high. Has any other city in history bounced back from losing two and a quarter million people?

Of course, 6 January is just a notional date based on forecasts by the Greater London Authority (GLA): we cannot know when it will actually happen, or even exactly what the peak was.

But we can be confident that this phenomenon is happening. So, let's take a look at how things have changed.

1. How did we get here?

It was the 18th century when London overtook Constantinople (Istanbul, as it is today) to become the biggest city in Europe; after that, huge Victorian growth saw it become the biggest city the world had ever seen. By 1939, it had been overtaken by New York, but was still the second biggest in the world. But today, depending on how you count, there are between 20 and 30 cities bigger than London.

The city's population peaked in 1939 at around 8.6m, and immediately began a rapid fall. At first that was because of the evacuations, the Blitz, and people going off to serve in the war – but the surprising thing is how fast the population continued to fall after the war. By the early 1990s, London had lost a quarter of its population, the equivalent of Birmingham, Edinburgh, Cardiff and Belfast all leaving town. London lost twice as many people as Detroit did.

What went wrong? Well, mostly it was deliberate. Forty years before the war Ebenezer Howard had asked, “The people, where will they go?” The answer, it turned out, was mostly not garden cities, it was to London. In huge numbers.

That was seen as a huge problem – in 1928 Clough Williams-Ellis compared the city’s sprawl to an octopus, devouring rural England. In 1938 Sir Anderson Barlow began his Commission into the redistribution of the Industrial Population, and would say, “The continued drift of population to London and the Home Counties constitutes a social, economic and strategic problem which demands immediate attention.”

Out of these concerns came the Abercrombie Plan, New Towns, the Greenbelt, and a ban on office developments – a deliberate policy of constraint and dispersal that reversed the growth of one of the world’s great cities. It has taken London 75 years to recover from these blows. Now the Greater London Authority estimates that, at some point on 6 January, probably in one of London’s busy maternity wards, we will be joined by the 8,615,246th Londoner.

In 1939 London was the largest city in a global trading empire of half a billion people. Today it is again the largest city and main commercial centre in a trading block of half a billion people. But while the British empire in 1939 still included a quarter of the world’s population, the EU now has only 7 per cent.

London dominates the UK population less than it did, too. In 1939, 18 per cent of the UK’s population lived in London, compared to only 13 per cent today.

2. Who are we?

Country of Birth of London residents. Source: Quod.

In 1939 London was overwhelmingly white. Only 2.7 per cent of us had been born abroad, and nearly half of those came from Ireland (even then, mind you, the next biggest nationality was Polish).

Today, around 37 per cent of Londoners were born abroad. The city’s rebirth quite simply would never have happened without immigration, although the biggest source of growth today is births.

We’re healthier too – in 1939 there was no NHS, London still choked on smog, and even before war broke out the average life expectancy was only 62 years. It’s no wonder that pensions seemed more affordable then.

Today Londoners can expect to live to 82, and while London remains a very young city overall, the population pyramid below shows we now have fewer teenagers and more pensioners. We also have more adult men – in 1939 there was still a “missing generation” from the First World War.

In 1939 statutory education only went up to age 14; so while we still use many old Victorian primary schools, in 1939, most of London’s 500 or so secondary schools had yet to be built. We need a similar wave of new schools now, with 133,000 more places needed in just the next four years.

Before the war barely 2 per cent of people went to university, and almost all of them were men. In London today it's 43 per cent – and a majority of them are women. London’s rebirth has been built on a high-skill, high-wage economy: the GLA forecasts that 90 per cent of all net new jobs will need a degree.

The number of people working in London hasn’t changed that much, but the industries we work in have. In 1939 around one in three people worked in manufacturing: London was still a major industrial city, and a quarter of million people worked in clothes-making alone. Almost as many worked in paper making as had “professional” jobs.

Now 90 per cent of these manufacturing jobs have gone: a million old jobs replaced by a million new jobs in services. Most people now work in industries that scarcely existing in 1939, including 250,000 working in IT. Another quarter of a million now work in hotels and restaurants – in 1939 tourism barely existed.

It is this ability for reinvention that has meant one of the biggest financial centres in the world has shrugged off the financial crisis: instead it's piled on jobs in tech, media and business services.

3. How do we travel?

In 1939, motor omnibuses had already largely replaced horses, and were starting to replace electric trams, too. But horse-drawn freight drays were still a common sight. The remarkable “multi-storey horse park” in Paddington still housed 500 working horses over three floors.

Hardly anyone had a car. There were only 2m private cars in the whole of Britain (25 people per car), compared to 2.6m cars in London alone today. There was still plenty of traffic, though, and rush hour speeds in central London have changed very little. Our roads are much safer, though: in 1939 1,187 people died on London’s roads, compared to only 132 people last year.

There is a perception (borrowed from America), that London’s huge 1930s suburbs grew up around the car, but in fact they were originally as much about the growth of the Underground and the bus. The 1930s saw the birth of mass commuting as we know it – the number of people travelling into central London for work had doubled in the previous 20 years. Bus use had grown to around 2.2bn journeys a year. It's now nearly back at those levels, at 2.1bn journeys a year.

Walking and cycling, however, have fallen dramatically – in 1939 they were one of the main ways many people got around. There are no exact figures, but cycling levels now are an order of magnitude lower than in 1939, despite the recent resurgence.

Perhaps the most remarkable change is in use of the Underground. In 1939, the tube was still divided into first and third class carriages, and even retained a few steam locomotives. There were no Jubilee or Victoria lines, and large chunks of the Central and Northern were still under construction. The London Passenger Transport Board had only just taken over responsibility from the private firms that started the Underground.

In 1939 there were 500m new journeys a year. Today we ​are hitting new records, with 1.3bn journeys and rising.

And aviation? Just 26 years after the invention of the plane, the world’s busiest international airport was… Croydon.

4. Where do we live?

The physical fabric of London has changed in many ways. In 1939 St Paul’s was still the tallest building in London, and had been for more than 200 years: it was still a city that Canaletto would still have recognised. Now St Paul’s is only the 41st tallest building in the London. Consider those under construction or with planning permission already granted, and it's clear it may soon not even make the top 100.

House prices have grown extraordinarily. While incomes have more than trebled in real terms, homes cost 15 times more in today’s money. In 1939 the average home cost around three years’ salary; now it is more like 16 years salary.

Tenure of London homes. Source: Quod.

Despite housing being more affordable in the 1930s, most people rented. The growth of the “property-owning democracy” was really only just beginning, and statutory provision of social housing was quite new, too. In 75 years private renting in London has more than halved, from 58 per cent of households to 26 per cent now. Nonetheless, the pressures of the housing crisis mean we are heading back to the future.

Source: Quod.

This map shows how London’s population has decentralised. The boroughs are distorted according to their 1939 population, and coloured to show how much this changed to today. What is clear is that the inner boroughs have shrunk, and the outer ones have grown.

This process had already gone a long way by 1939, but continued long after, as post-war “slum” clearance replaced very high density inner London Victorian housing with lower density social estates. Londoners are now much more evenly distributed across the city than before.

By the start of the Second World War, London had just witnessed a frenzied decade of housebuilding, creating the shape of suburban London as we know it today. This next map shows pre-war areas in blue, and post war areas in red: the shape of London has hardly been allowed to change since 1939, although the redevelopment of docklands stands out.

Thise second map shows the areas of London that were newly built in 1939 in blue: well over half a million new homes were built in the 1930s. In red are the bits that are new today, much of it commercial rather than housing development. Since 1992, when London started to grow again, housebuilding has been barely a quarter of the 1930s rate.

So, London is back to its peak, and while it has changed in so many ways, it faces some of the same challenges. Just like 75 years ago, we have extraordinarily fast population growth, with commuting patterns and housing pressure spilling way beyond the city’s boundaries.

Last time we responded by choking off that growth and imposing 50 years of decline. What do we choose this time? Can we invest and support growth?

Barney Stringer is a director of regeneration consultancy Quod, who writes about cities, economics and infrastructure. This article was originally posted on his blog here.

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