Mr Scargill, 74, who was the NUM’s president for 20 years until July 2002, has occupied the Barbican apartment, rented from the Corporation of London, since June 1982.
The rent and associated expenses were paid by the union until 2011, except for a period between 1985 and 1991 when Mr Scargill met them out of his own pocket.
The NUM’s counsel, Nicholas Davidson QC, said that the case was not about whether anyone thought that any particular obligation ought to exist – but whether it did exist.
If it did, Mr Scargill was entitled to have the benefit of it.
He told Mr Justice Underhill that the action concerned whether the union was obliged to meet the costs of the use of the flat for the rest of Mr Scargill’s life and the lifetime of his widow, should he leave one.
The hearing is due to last a week.