Huge nine-storey Knightsbridge mansion 25 times bigger than the average Brit home is on sale for £25million - and there's one very deep catch
Rachel Newton
Updated on March 15, 2026
A HOUSE at the centre of one of London's biggest planning controversies has been put on the market for £25million - complete with a giant hole in the garden.
On the face of it the Grade II listed Georgian home in Knightsbridge has just about everything a wealthy buyer looks for in the super-prime central London property market.
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It has a sought-after address, boasts one of the area's largest private gardens and has the potential to be turned into a nine-storey mansion which is 25 TIMES the size of the average English home.
But the property has attracted anger from neighbours for almost a decade after the garden was turned into an eyesore by its conman owner.
Achilleas Kallakis began digging a mega-basement in the mid-2000s to house a swimming pool, spa, cinema and car lift.
The project was abandoned when workers downed tools in 2008, and in 2011 the property was sold to its current owner for £28million.
Six years on it remains an unfinished building site, with a 30ft deep crater the size of two tennis courts dominated by more than a dozen 60ft piles.
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The registered owner, British Virgin Islands-based 31 Brompton Square Ltd, has now put the property on the market for £3million less than it paid.
Estate agent Savills describe it as an "exceptional opportunity to create a spectacular family home of over 22,000 sq ft in this elegant Knightsbridge garden square".
It adds: "The new proposals provide nine floors of living spaces including a swimming pool, underground car parking with car lift, double-height reception spaces and an impressive entrance hall."
Plans for a lavish four-storey mega-basement complex were approved by the Royal Borough of Kensington and Chelsea last year, despite the council's policy to restrict basement excavations to one storey.
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The whole of the lowest floor is given over to a vast underground garage with car lift and turntable, according to the architect's plans.
Above that will be the swimming pool and gym. Basement -2 will be a "family space" along with music room, music store and cinema.
Basement -1 will have three guest bedrooms with en-suite bathrooms along with a kitchen and laundry room.
The original home above ground will have grand entertaining rooms with a huge master bedroom suite taking up the whole of the second floor. The top two storeys will have five further bedrooms.
The ground floor will have a large kitchen, reception room and formal dining room as well as the entrance to the garden.
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Brompton Square residents have described the long-running planning saga as a "nightmare".
One neighbour said it had "been a plague on our lives for eight years".
They added: "We've had problems with subsidence from the dig. We don't overlook a garden in a lovely London neighbourhood but a vast chasm into a building site."
Tony Knight, who lives nearby, said the hole was a "complete mess" and described it as "probably almost as deep as the Führerbunker in Berlin".
The saga dates back to a 2005 planning application from Achilleas Kallakis, who snapped up the grand home as part of a haul of trophy assets.
In 2013 he was jailed for seven years after posing as a Mayfair property tycoon to dupe banks out of £740million with forged documents, sham legal letters and bogus guarantees.
His sentence was later extended by four years.
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