The billionaire businessman John Caudwell, owner of the Phones 4 U mobile and telecommunications business seems intent on building an urban palace rather than simple basement extension with plans to turn two mansions in one of the most upmarket parts of London into a single dwelling  almost the size of Westminster Cathedral. An ‘iceberg’ extension will be created by excavating beneath the existing properties to allow for a vast games room, swimming pool, sauna, kitchen, salon, media room, plant room and car park.

 Amounting to 180ft in length stretching  and joining both properties beneath their gardens, which back on to each other in Mayfair. The result will be a single property of some 50,000 sq ft. The ‘iceberg’ extension alone will cover 14,000 sq ft.Once complete, the mansion will have 12 bedrooms, there are five in each house already and the plans include two more in the underground extension.

 With property prices for super-prime homes in Mayfair at around £5,000 per sq ft, the finished home  could be worth £250million. In the 1960s it was a members club and, according to its history, was frequented by ‘dubious  gangland characters’, footballers and celebrities. It was bought  by Prince Jefri, brother of the Sultan of Brunei, in 1992 for a reported £18million.

 Iceberg homes, are becoming common among the ultra-rich, but are controversial because of the inconvenience they can cause to neighbours during the building work.