A house is not a home until it has it's own a helipad.

In 2008, to spend £50m on a new house seems excessive to say the least but to then splurge another £30m on doing it up  is mind boggling. But the super-prime section of the London property market is an exclusive world, with laws of its own. Indeed, the new Kazakh owners of the grandest house on The Bishops Avenue, north London's billionaires' row, believe they bagged a bargain when they bought the Toprak Mansion earlier this month.

But the decor, it seems, is not right! Despite the five reception rooms, nine main bedrooms and 16 bathrooms, all spread over 23,000 sq ft, the place is to too small. So, although Toprak, with his woollen rugs, one of the most expensive new-build properties sold in Britain at the time, this house has probably been lived in for less than a week or so since it was completed in 2001, the owners are calling in the builders and the bespoke rug designers.

By the time they've finished, as well as all the basics de rigueur for the self-respecting billionaire such as wireless audiovisuals, pressurised purified water on tap and automatic security shutters, they will also build a new 30-seat cinema, squash and tennis courts, a billiards room, a beauty salon, a 24-carat gold-plated whirlpool bath, a new staff lift and a small river, complete with canoe. Even the helicopter gets its own lift: the helipad in the garden will sink into the ground and the roof will slide across the top.

The end result, expected to cover 42,000 sq ft, looks certain to outclass its next-door neighbour, Lakshmi Mittal, whose own 25,000 sq ft house, Summer Palace, can be peered into from the mansion's 80ft main reception room. (Not that Mittal is often there: the Indian steel magnate spends most of his time at his other home in Kensington Palace Gardens, west London.)

But where are the carpets and rugs? Currently being imported from india and expected to be laid on every floor in the mansion.