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London is growing so quickly that it could need homes and jobs for another 1.5 million people by 2036 — the equivalent of providing for an extra population the size of Birmingham and Coventry combined.

Now, for the first time, city planners are aiming to keep future growth within London’s boundaries — saying that despite pressures, the capital is a low-density city compared with its international peers.

Over the past decade, says the report, London has built too few homes, leading to the crisis. It also reveals that the boroughs build barely one per cent of new homes, while the capital is likely to need a forest of new towers, some of which will be three times more crowded than Hong Kong’s most heavily populated districts - and 37 times denser than London’s present levels.

THE TOWERING CHALLENGE

London’s soaring population will soon outstrip its historic peak of 8.61 million in 1939, according to a new report, due out on Friday, for Mayor Boris Johnson.

By 2036, it could well reach 10 million. That means fitting in up to 1.5 million extra people — about the size of the populations of Birmingham and Coventry combined — and all the new infrastructure that will be required, including more houses, employment opportunities, shops and better transport links.

The capital will have to build the equivalent of eight new Canary Wharfs to provide the jobs and 50,000 new homes will have to be built every year to house 70,000 extra people.

The predictions follow a recent Greater London Authority survey which revealed that what worries Londoners most is the shortage of affordable housing in the city.

Year after year we have failed to build enough homes to meet demand — fewer than 23,000 a year between 2009 to 2014 when we should have been building 50,000.

The Mayor’s report, the Good Growth Agenda, which involved his closest advisers, looks at how London can grow while retaining the qualities that make the city great.

While most development should be kept within the green belt, the authors say, there should also be selective green belt use and the creation of new outer London “Metro-Lands”.

WHERE WILL THEY ALL GO?

A key finding in the report is that London’s councils have virtually ceased to build new properties.

In the mid-Sixties and Seventies, councils built three quarters of all the capital’s new homes, but last year they constructed just 310, barely one per cent of the 26,843 new homes.

London councils own 40 per cent of the land considered suitable for building homes. A big difference is that council house building was once heavily subsidised — today it is not.

The report shows that local planning offices do not have enough planners or money. A staggering 91 per cent of London boroughs say they need more “place-shaping” skills.

It also makes clear that the public sector is too slow at delivery and suggests that, instead of councils calling in expensive consultants to plug the planning shortfall, incurring “unnecessary costs”, the Mayor should train a specialist taskforce of “place-shaping practitioners” to send out to the boroughs at affordable rates, starting this year.

The report also says smaller architectural practices should get a chance to be involved in larger-scale schemes, to encourage more innovation.

The Mayor’s report says there are 5,000 sites identified as suitable for new homes in London, covering nearly 20,000 acres. However, it says that land only has capacity for 470,000 new properties over the coming two decades.

The Mayor’s advisers on public space say: “Londoners want to live in connected places that are lively, full of energy, and not on ‘island’ developments.” They say, according to the London Plan, that “81 per cent of housing capacity is in or around town centres”.

An estimated 154,000 to 218,000 homes could be built in town centres that already have the shops, offices, doctors, schools and transport everyone needs. According to a recent survey, two thirds of Londoners live less than five minutes’ walk from a high street.

BUILD BIGGER AND TALLER

One section of the report, called Growing London, has some eye-catching statistics on housing density.

Compared with other major cities around the world, London has space to spare.

Its current population density is five times lower than in the 1830s. In 1816, density was about 297 people per hectare (about 2.4 acres). Now it is 73 a hectare, though some areas are up to 271 a hectare. If we lived at the 1816 density levels, there would be 35 million people in London.

In contrast, New York has a peak density of 585 per hectare, while Hong Kong’s peak is 1,111 a hectare.

Tower blocks can easily reach 1,000 people per hectare — a single tower can contain 600 homes. But going from one extreme to the other, there are 263 towers higher than 20 storeys planned for London, and 33 developments with population densities above 1,000 per hectare.

Most worrying is that there are “projects being proposed in London reaching densities of more than 3,000 homes per hectare”. That would produce a living density more than three times the peak density of Hong Kong. The report does not say where these developments are.

The report takes it as a given that to hit housing targets, London must build high. But while it acknowledges that some experts disagree, and that life quality at these densities needs to be better understood, it does not say how that understanding should be achieved.

It’s strangely unclear why this informative, provocative report was commissioned at the end of Mr Johnson’s two terms of office, rather than at the start, since the housing crisis was well documented in 2004. Nor can we guess what the new mayor, who will be elected in May, will make of the findings.

But whatever is decided now, says the report, “will have exponential and lasting implications for the ongoing affordability and social sustainability of the city”.