While the billionaires of Kensington dig ever deeper to excavate multi-storey pleasure bunkers of private cinemas, swimming pools and car museums beneath their homes, there are plans afoot in an unlikely part of west London for the mega-basement to end all mega-basements. On a scruffy patch of land in suburban Hounslow a mile from Heathrow airport, surrounded by cosy crescents of semi-detached homes, planning permission has been granted to Formal Investments Ltd to dig out the biggest underground space in the UK. It will not be topped with an oligarch’s mansion, but a brand new park for Londoners.



Driving along the busy dual carriageways that hem the site of Rectory Farm, you would have little idea that beneath this unremarkable stretch of former agricultural land, frequented by fly-tippers and the occasional travelling circus, lies a valuable bounty. Like much of the city’s green belt, this 44-hectare (109 acres) swathe of land has been off-limits for years, being privately owned, too small to farm and protected from development. Yet beneath the topsoil lies £50-60m worth of gravel – an essential ingredient for the construction industry as an aggregate in concrete, which usually has to be trucked into the city from far-flung quarries or dredged from the North Sea.

The council has identified the site as a strategic location for aggregate extraction, but previous planning applications for an open-cast mine failed for numerous reasons – from air pollution to the likelihood of creating lakes that would attract nesting birds, a dangerous arrival in the middle of the Heathrow flightpath.

An ingenious solution has finally come from a surprising source, in the form of architecture firm Carmody Groarke, the fashionable designers of galleries, pop-up restaurant pavilions and luxury homes – one of which features a tunnel from the main house to a lakeside hideaway. Here in Hounslow, they’ve been able to let their penchant for digging run wild.

London’s billionaires are digging ever deeper to create space for swimming pools, gyms and car parking. Photograph: View Pictures/Rex/Shutterstock

“It seemed like a no-brainer,” says Kevin Carmody, sitting in his Covent Garden studio, surrounded by big models of forthcoming museum projects for Dorset, Manchester and the Lake District. “Why not find a way of opening up the site as a public park, while secretly excavating out the valuable gravel below, and make the leftover underground space pay for the project, as well as funding the park in perpetuity?” The plan is as conceptually simple – and technically complex – as that.

Working with engineers Arup, they plan to use a method of “top-down” construction borrowed from big towers in the City (where both space and time for construction are at a premium) to liberate the subterranean booty with minimal disruption. Dividing the site into segments of around 100 metres squared to allow the park to be used while construction continues, they will first scrape back the topsoil before drilling great concrete columns into the ground, then cast a concrete slab on top and return the soil, landscaping the park with raised berms and pathways. The gravel can then be excavated over time and extracted via access ramps with a concrete batching plant on site for the project’s own construction.

“It’s usually expensive to build top-down,” says Carmody, “but here we’re able to make savings because the structure is made out of the very stuff we’re digging on site.”

The ‘top-down’ construction plans for Rectory Farm. Illustration: Carmody Groarke

Once excavation is complete in around 15 years time, it will leave behind a 180,000 sq metre warehouse space, almost twice the size of the largest logistics shed in the country. The income from this space will be used to pay for the upkeep of the park, as agreed in the planning permission. A final use for this vast basement has yet to be determined, but it could host everything from long-term museum and archive storage, to logistics space and potentially even amenities like a theatre, gym or pool for the nearby school in its 10-metre deep cavern.

The park itself, which at 110 acres will be around the size of St James’s and Green Park combined, has been designed by landscape practice Vogt. In the tradition of London’s royal parks, it will be bisected by a 1km-long tree-lined avenue and further divided into pockets by raised berms and drainage channels, marking the column grid below ground. Developed in consultation with Sport England, it will also host a mixture of pitches for football, hockey and cricket, with the berms creating more intimate outdoor “rooms” and providing acoustic buffers so players can hear the referee’s whistle.

While rural quarries are often repurposed after their useful lives – such as the transformation of a Cornish clay pit into the Eden Project greenhouse complex, or some gravel pits in Preston into the Brockholes wetland reserve – this is the first time an active quarry in an urban location will also serve as a park.

Providing around 3m tonnes of gravel, the Rectory Farm plans go a long way to fulfilling London’s demand for sustainably-sourced aggregates, providing 70% of the mayor’s target over the next 25 years. Particularly if Heathrow’s third runway finally gets the go-ahead, it would ensure a huge reduction in miles travelled to haul the gravel to site, while simultaneously opening up this patch of green belt land to the public in an area with a dearth of open space.

As outer London boroughs wring their hands over green belt land, while losing industrial space for warehousing and logistics to the insatiable march of housing, this ambitious project provides a clever model that they might do well to learn from.

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