Mittal, who bought 6 Palace Green for a reported £117m in 2008, is now thought to be willing to sell the property for just over £100m.
The Georgian-style property comes with extensions, bedroom suites and servants’ quarters.
It was originally bought from hedge fund boss Noam Gottesman to provide a base for Mittal’s son Aditya. However, it is thought that he never moved in and the property has sat unoccupied for five years.
Mittal lives in a smaller property on the same street. He has also bought another neighbouring building, the former Israeli embassy, for his daughter.
Although the Mittals do not own the house directly, it is thought they control the Virgin Islands-registered Tamzen Ltd. which possesses the deeds.