The Italian tax authorities are investigating the estate of Gianni Agnelli, the late chairman of Fiat, following a fierce family dispute over his assets that has exposed the internal dynamics of Italy’s wealthiest industrial dynasty.

The probe follows allegations in 2007 by Margherita Agnelli de Pahlen, Mr Agnelli’s daughter, that she had been denied part of her inheritance from the estate of her father because some €1bn ($1.4bn) in undeclared assets had been held in Swiss bank accounts.