• Reade Griffith ordered to pay fee to install two-storey basement
  
• Build will house pool and spa and likely add £10million to house value
  
• Experts said the levy is unprecedented for homeowners and is  normally reserved for large-scale developments 
• Basement equivalent to eight average-sized new-build family homes
  
• Kensington and Chelsea Council said it will be used for affordable housing

By Larisa Brown and Ben Spencer

PUBLISHED: 20:06 EST, 21 August 2013 | UPDATED: 20:06 EST, 21 August 2013

A hedge fund manager has been ordered to pay a fee of more than £800,000 to create a huge two-storey underground basement below his mansion.

The unprecedented levy on a basement excavation has shocked property experts and appears to mark the beginning of a council fightback against the creation of ‘iceberg homes’ in exclusive areas.

Multi-millionaire Reade Griffith, 48, and his wife Elizabeth, 42, plan to build a vast subterranean extension underneath two adjoining Kensington townhouses at an estimated cost of £4million.

Housing a swimming pool, spa and ‘treatment ‘area’ it is likely to add £10million to the value of the property.

At about 900 square metres, the basement would be the equivalent to eight average-sized new-build family homes.

But due to the sheer scale of the extension, Kensington and Chelsea Council asked for a one-off fee of £825,000 when it granted planning permission earlier this month. According to planning documents seen by the Daily Mail, the fee will go towards affordable housing elsewhere in the borough.

Such payments – known as ‘Section 106 agreements’ – are normally confined to large-scale commercial developments of housing estates. It is highly unusual for them to be applied to single private planning applications.

Their extension to domestic homes could be seen as a new tax on wealthy homeowners, who already pay 7 per cent stamp duty on property purchases over £2million, and could enrage well-heeled residents looking to expand their properties in exclusive parts of  London.

The project has been applied for in the name of Mrs Griffith, who owns one of the properties. Her husband, founder of Polygon Investment Partners, once one of London’s most high-profile funds, owns the neighbouring house through a company. The two properties have 13 bedrooms between them.

The proposed development will see the build of a ‘double level basement extension under both buildings and extending under the small front and rear gardens whilst respecting the tree protection areas’, according to planning documents.

Architects’ drawings show how the vast house will include a plunge pool, spa pool, a cinema room, games room, bar and even a wine store.

Both of the houses are listed as ‘buildings of local interest’ in an area that has ‘become highly desirable as a residential location’.

The proposal reads: ‘Our clients wish to create two dwellings suitable for contemporary living, and to enhance the appearance of the buildings by reinstating lost architectural detailing and adding an appropriately designed first floor extension’.

Stuart Robinson, head of planning at the CBRE, the global property agents, said the move by the council to ask for a fee to build the extension was unusual.

He said: ‘This is completely off the scale. You don’t normally get these agreements with residential applications.’

Gary Sector, legal director for law firm Addleshaw Goddard, said the sum appeared to be ‘unprecedented’ for a domestic renovation.

The planning application reflects the trend for London’s most wealthy homeowners to extend downwards after being faced with the high cost of moving house and the perception among many overseas buyers that London houses lack sufficient space.

Planning requests for ‘dig-downs’ have soared in Kensington and Chelsea in the last decade, rising from 13 in 2001 to 307 in 2012.

Some boroughs are now starting to fight back against giant basements amid fears about the noise and disruption caused.

Alan Waxman, founder of Landmass London, a residential designer and developer, said owners were unlikely to be put off by the council’s levy.

He said: ‘If they are building around 1,000 square metres that could be worth some £10million, so even if it cost £4million to do and the fee is £800,000 the owner could still double their money.’