The founder of Foxtons has been embroiled in a lengthy legal battle with the French government over whether he can finish his mega-basement for his vintage cars.

The French Embassy resides next door and challenged two certificates granted by the Royal Borough of Kensington and Chelsea.

It is unusual for such cases to reach the High Court, however, extravagant extensions are becoming more popular.

Stricter rules were placed on basement extensions that restrict how far they can stretch under a garden, limit them to a single storey in most cases, and ban developments under listed buildings altogether.