Welcome to my super-basement! Tycoon to get go-ahead for huge underground swimming pool, jacuzzi and wine store

A tycoon is hoping to extend his £9.1million mansion by creating a huge 500 square metre basement - to the fury of neighbours in his upmarket street.

Homeowners fear plans to create an underground lair with swimming pool, jacuzzi, wine store and a 'garden room' will create a major flooding risk.

The plans are set to be approved next month despite fierce opposition.

Impressive home: £9.1million property will have its basement extended nine-fold

Impressive home: £9.1million property will have its basement extended nine-fold

The property in Hampstead, north London, which is believed to be owned by hedge fund boss Trifon Natsis, is on one of the capital's most exclusive streets.

Neighbours fear the building works will cause two years of noise, vibrations and disruption.

The property, once owned by the Polish ambassador, already has a 57 square metre basement. However, in plans produced by Tony Fretton, a leading British architect, it will be extended to 495 square metres.

The one-and-a-half storey-high basement will be constructed below the garden and substantial works are also planned for the house, built in the 1900s.

Properties in exclusive Templewood Avenue, downhill from Hampstead Heath, are built on clay - which water cannot easily penetrate.

During heavy rain the drains overflow. If so much earth is dislodged by the extension, there are concerns there could be flooding.

Irving Yass, who has lived in the avenue for 30 years, said: 'This is designated as an area of moderate flood risk. The drains already can’t cope during storms.

Huge: Tycoon is to be given the go-ahead to build a 495 square metre underground basement

Huge: Tycoon is to be given the go-ahead to build a 495 square metre underground basement

We are worried that by building a huge underground structure you will obstruct the flow of water underground and we will suffer more flooding.'

Mr Yass, 75, a retired civil servant, is one of six neighbours who wrote to Camden council with concerns about the works. He said residents had been shown no hydrological report.

Emmanuel Harries, who has lived  in the avenue for 25 years, said: 'We received a letter saying they are going to drill underneath but apart from that we’ve heard nothing. There’s huge concern about vibrations from the digging and fears that this project will ruin the character of the street.'

The Redington/Frognal Conservation Area Advisory Committee claims the basement is 'oversized' and the Heath and Hampstead Society says the design is out of character with the conservation area. The society also raised concerns about the impact the basement may have on the local water table.

Camden council’s planning committee had been due to decide on the proposals last night but discovered that some objectors had not been informed of the meeting. It is now expected to approve the plans at the next meeting in three weeks.

A council report said: 'It is considered the proposed demolition and development are acceptable in design and scale and would preserve the character and appearance of the building, street scene and conservation area.'

As well as the basement work, the main house will be re-modelled to add a series of dormer windows studded into the roof and terraces at ground-floor and first-floor levels.

A side extension will be decorated with a terracotta balustrade and a white timber porch will be added to the front of the house.

Mr Natsis, co-founder of Brevan Howard Asset Management LLP, was unavailable for comment.