Operations at Crossrail's Stepney Green rail construction site
Operations at Crossrail's Stepney Green rail construction site © Bloomberg

The smooth running of great cities is magical. As with any conjuror’s trick, the delight and surprise comes from never knowing how it works and, in the case of London, the magic is maintained by what happens underground.

Much of what keeps the UK capital ticking over lies below the surface and there is more going on down there than ever before.

London’s global appeal means that the population has grown strongly in recent years and is expected to surpass its prewar population high by the end of this year, reaching 10m people by 2031. Supporting all those extra people means creating new infrastructure, and a lot of the city’s latest plans are happening underground.

Many Londoners don’t even know it is there, but it is essential for the city’s continuing popularity – and prosperity – in the coming years.

Substantial transport, power and sanitation projects are all under way to help cope with London’s expansion, while, in housing, London isn’t just growing outwards – it’s also growing downwards.

Increasing numbers of homeowners are seeking more space in the capital’s crowded housing market by digging out their basements – sometimes going down several storeys.

Meanwhile, London’s mayor, Boris Johnson, says the capital’s infrastructure schemes will “support the demands of our growing city”.

“These projects are absolutely vital to providing the many more homes Londoners need, and to support the city’s economic growth,” he says. “All these new neighbourhoods need to be underpinned with power, water and drainage systems.”

Some of the projects have the potential not just to support a larger London population in general, but to help boost house prices and new housebuilding in specific areas. Transport projects in particular can have a big effect. The flip side, however, is disruption to existing householders. All projects try to minimise this – the National Grid’s power tunnels run underneath north London roads specifically to avoid people’s homes as much as possible – but any kind of underground construction activity is likely to create subsidence above ground, according to Professor Robert Mair of the University of Cambridge.

An expert in underground tunnel engineering, Mair is an adviser on the Crossrail project, among others. “You can’t do any kind of underground construction without there being some movement. The only question is how much exactly,” he says.

Although some previous construction work beneath London’s streets has provoked considerable movement above ground – Mair cites the example of the Jubilee Line extension, when one building dropped by 5cm – most movement tends to be in the millimetres range.

In addition, these projects are not just the biggest London has ever seen, they are also the deepest. At some points they will reach down almost as deep as the foundations of London’s tallest towers, such as the Shard.

Kate Allen is the FT’s property correspondent

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