An Israeli diamond billionaire has bought the most expensive new property ever sold in Britain -- a $70 million (35 million pound) home with a bullet-proof front door costing $100,000, real estate dealers said on Tuesday.

The seven-bedroom house in the exclusive north London district of Hampstead boasts a $1.5 million stone staircase constructed using 150-year-old carving techniques and an indoor swimming pool with gold-plated mosaic tiles.

The Palladian-style home also features a gym, sauna, ballroom and cinema, a private hair salon and a one-tonne bathroom basin carved from a single piece of white Iranian onyx.

It has been bought by Lev Leviev, a 51-year-old Israeli businessman best known for his diamond trading company and who is estimated to be worth $6.5 billion.